[PATCH v9 00/12] kthread: Kthread worker API improvements

STALE3695d

Revision v9 of 4 in this series.

33 messages, 3 authors, 2016-06-29 · open the first message on its own page

[PATCH v9 00/12] kthread: Kthread worker API improvements

From: Petr Mladek <pmladek@suse.com>
Date: 2016-06-16 11:17:44

I send the kthread worker API improvements separately as discussed
in v6, see
https://lkml.kernel.org/g/20160511105224.GE2749@pathway.suse.cz
They seem to be ready for inclusion in 4.8.

I will send the conversion of the particular kthreads once
the API changes are in some maintainers three (-mm?) and
visible in linux-next. If nobody suggests some other approach.

Also I plan to continue with conversion of more kthreads.

Just to remember. The intention of this patchset is to make
it easier to manipulate and maintain kthreads. Especially, I want
to replace all the custom main cycles with a generic one.
Also I want to make the kthreads sleep in a consistent
state in a common place when there is no work.


Changes against v8:

  + Fixed names of DEFINE() and INIT() macros. Please, find
    more comments in the 2nd patch.


Changes against v7:

  + Fix up all names of functions and macros to be prefixed
    by kthread_/KTHREAD_; This is done also for existing
    functions and macros, see the first two patches


Changes against v6:

  + no changes.


Changes against v5:

  + removed spin_trylock() from delayed_kthread_work_timer_fn();
    instead temporary released worked->lock() when calling
    del_timer_sync(); made sure that any queueing was blocked
    by work->canceling in the mealtime

  + used 0th byte for KTW_FREEZABLE to reduce confusion

  + fixed warnings in comments reported by make htmldocs

  + sigh, there was no easy way to create an empty va_list
    that would work on all architectures; decided to make
    @namefmt generic in create_kthread_worker_on_cpu()

  + converted khungtaskd a better way; it was inspired by
    the recent changes that appeared in 4.6-rc1


Changes against v4:

  + added worker->delayed_work_list; it simplified the check
    for pending work; we do not longer need the new timer_active()
    function; also we do not need the link work->timer. On the
    other hand we need to distinguish between the normal and
    the delayed work by a boolean parameter passed to
    the common functions, e.g. __cancel_kthread_work_sync()
    
  + replaced most try_lock repeat cycles with a WARN_ON();
    the API does not allow to use the work with more workers;
    so such a situation would be a bug; it removed the
    complex try_lock_kthread_work() function that supported
    more modes;

  + renamed kthread_work_pending() to queuing_blocked();
    added this function later when really needed

  + renamed try_to_cancel_kthread_work() to __cancel_kthread_work();
    in fact, this a common implementation for the async cancel()
    function

  + removed a dull check for invalid cpu number in
    create_kthread_worker_on_cpu(); removed some other unnecessary
    code structures as suggested by Tejun

  + consistently used bool return value in all new __cancel functions

  + fixed ordering of cpu and flags parameters in
    create_kthread_worker_on_cpu() vs. create_kthread_worker()

  + used memset in the init_kthread_worker()

  + updated many comments as suggested by Tejun and as
    required the above changes

  + removed obsolete patch adding timer_active()

  + removed obsolete patch for using try_lock in flush_kthread_worker()

  + double checked all existing users of kthread worker API
    that they reinitialized the work when the worker was started
    and would not print false warnings; all looked fine

  + added taken acks for the Intel Powerclamp conversion
    

Changes against v3:

  + allow to free struct kthread_work from its callback; do not touch
    the struct from the worker post-mortem; as a side effect, the structure
    must be reinitialized when the worker gets restarted; updated
    khugepaged, and kmemleak accordingly

  + call del_timer_sync() with worker->lock; instead, detect canceling
    in the timer callback and give up an attempt to get the lock there;
    do busy loop with spin_is_locked() to reduce cache bouncing

  + renamed ipmi+func() -> ipmi_kthread_worker_func() as suggested
    by Corey

  + added some collected Reviewed-by

  
Changes against v2:

  + used worker->lock to synchronize the operations with the work
    instead of the PENDING bit as suggested by Tejun Heo; it simplified
    the implementation in several ways

  + added timer_active(); used it together with del_timer_sync()
    to cancel the work a less tricky way

  + removed the controversial conversion of the RCU kthreads

  + added several other examples: hung_task, kmemleak, ipmi,
    IB/fmr_pool, memstick/r592, intel_powerclamp

  + the helper fixes for the ring buffer benchmark has been improved
    as suggested by Steven; they already are in the Linus tree now

  + fixed a possible race between the check for existing khugepaged
    worker and queuing the work
 

Changes against v1:

  + remove wrappers to manipulate the scheduling policy and priority

  + remove questionable wakeup_and_destroy_kthread_worker() variant

  + do not check for chained work when draining the queue

  + allocate struct kthread worker in create_kthread_work() and
    use more simple checks for running worker

  + add support for delayed kthread works and use them instead
    of waiting inside the works

  + rework the "unrelated" fixes for the ring buffer benchmark
    as discussed in the 1st RFC; also sent separately

  + convert also the consumer in the ring buffer benchmark


I have tested this patch set against the stable Linus tree
for 4.7-rc2.

Comments against v8 can be found at
https://lkml.kernel.org/g/1465480326-31606-1-git-send-email-pmladek@suse.com


Petr Mladek (12):
  kthread: Rename probe_kthread_data() to kthread_probe_data()
  kthread: Kthread worker API cleanup
  kthread/smpboot: Do not park in kthread_create_on_cpu()
  kthread: Allow to call __kthread_create_on_node() with va_list args
  kthread: Add kthread_create_worker*()
  kthread: Add kthread_drain_worker()
  kthread: Add kthread_destroy_worker()
  kthread: Detect when a kthread work is used by more workers
  kthread: Initial support for delayed kthread work
  kthread: Allow to cancel kthread work
  kthread: Allow to modify delayed kthread work
  kthread: Better support freezable kthread workers

 Documentation/RCU/lockdep-splat.txt         |   2 +-
 arch/x86/kvm/i8254.c                        |  14 +-
 crypto/crypto_engine.c                      |  16 +-
 drivers/block/loop.c                        |   8 +-
 drivers/infiniband/sw/rdmavt/cq.c           |  10 +-
 drivers/md/dm.c                             |  10 +-
 drivers/media/pci/ivtv/ivtv-driver.c        |   6 +-
 drivers/media/pci/ivtv/ivtv-irq.c           |   2 +-
 drivers/net/ethernet/microchip/encx24j600.c |  10 +-
 drivers/spi/spi.c                           |  18 +-
 drivers/tty/serial/sc16is7xx.c              |  22 +-
 include/linux/kthread.h                     |  90 +++-
 kernel/kthread.c                            | 612 ++++++++++++++++++++++++----
 kernel/smpboot.c                            |   5 +
 kernel/workqueue.c                          |   2 +-
 sound/soc/intel/baytrail/sst-baytrail-ipc.c |   2 +-
 sound/soc/intel/common/sst-ipc.c            |   6 +-
 sound/soc/intel/haswell/sst-haswell-ipc.c   |   2 +-
 sound/soc/intel/skylake/skl-sst-ipc.c       |   2 +-
 19 files changed, 685 insertions(+), 154 deletions(-)

-- 
1.8.5.6

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[PATCH v9 01/12] kthread: Rename probe_kthread_data() to kthread_probe_data()

From: Petr Mladek <pmladek@suse.com>
Date: 2016-06-16 11:17:51

A good practice is to prefix the names of functions by the name
of the subsystem.

This patch fixes the name of probe_kthread_data(). The other wrong
functions names are part of the kthread worker API and will be
fixed separately.

Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 include/linux/kthread.h | 2 +-
 kernel/kthread.c        | 4 ++--
 kernel/workqueue.c      | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index e691b6a23f72..c792ee1628d0 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h

@@ -44,7 +44,7 @@ bool kthread_should_stop(void);
 bool kthread_should_park(void);
 bool kthread_freezable_should_stop(bool *was_frozen);
 void *kthread_data(struct task_struct *k);
-void *probe_kthread_data(struct task_struct *k);
+void *kthread_probe_data(struct task_struct *k);
 int kthread_park(struct task_struct *k);
 void kthread_unpark(struct task_struct *k);
 void kthread_parkme(void);

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 9ff173dca1ae..0bec14aa844e 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c

@@ -138,7 +138,7 @@ void *kthread_data(struct task_struct *task)
 }
 
 /**
- * probe_kthread_data - speculative version of kthread_data()
+ * kthread_probe_data - speculative version of kthread_data()
  * @task: possible kthread task in question
  *
  * @task could be a kthread task.  Return the data value specified when it

@@ -146,7 +146,7 @@ void *kthread_data(struct task_struct *task)
  * inaccessible for any reason, %NULL is returned.  This function requires
  * that @task itself is safe to dereference.
  */
-void *probe_kthread_data(struct task_struct *task)
+void *kthread_probe_data(struct task_struct *task)
 {
 	struct kthread *kthread = to_kthread(task);
 	void *data = NULL;

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index e1c0e996b5ae..64a9df2daa2b 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c

@@ -4249,7 +4249,7 @@ void print_worker_info(const char *log_lvl, struct task_struct *task)
 	 * This function is called without any synchronization and @task
 	 * could be in any state.  Be careful with dereferences.
 	 */
-	worker = probe_kthread_data(task);
+	worker = kthread_probe_data(task);
 
 	/*
 	 * Carefully copy the associated workqueue's workfn and name.  Keep

-- 
1.8.5.6

[PATCH v9 02/12] kthread: Kthread worker API cleanup

From: Petr Mladek <pmladek@suse.com>
Date: 2016-06-16 11:17:59

A good practice is to prefix the names of functions by the name
of the subsystem.

The kthread worker API is a mix of classic kthreads and workqueues.
Each worker has a dedicated kthread. It runs a generic function
that process queued works. It is implemented as part of
the kthread subsystem.

This patch renames the existing kthread worker API to use
the corresponding name from the workqueues API prefixed by
kthread_:

__init_kthread_worker()		-> __kthread_init_worker()
init_kthread_worker()		-> kthread_init_worker()
init_kthread_work()		-> kthread_init_work()
insert_kthread_work()		-> kthread_insert_work()
queue_kthread_work()		-> kthread_queue_work()
flush_kthread_work()		-> kthread_flush_work()
flush_kthread_worker()		-> kthread_flush_worker()

Note that the names of DEFINE_KTHREAD_WORK*() macros stay
as they are. It is common that the "DEFINE_" prefix has
precedence over the subsystem names.

INIT_() macros are similar to DEFINE_. Therefore this patch
renames:

KTHREAD_WORKER_INIT()		-> INIT_KTHREAD_WORKER()
KTHREAD_WORK_INIT()		-> INIT_KTHREAD_WORK()

Note that INIT() macros and init() functions use different
naming scheme. There is no good solution. There are several
reasons for this solution:

  + INIT() macros are used only in DEFINE() macros. They
    should use the same naming scheme.

  + init() functions are used close to the other kthread()
    functions. It looks much better if all the functions
    use the same scheme.

  + There will be also kthread_destroy_worker() that will
    be used close to kthread_cancel_work(). It is related
    to the init() function. Again it looks better if all
    functions use the same naming scheme.

  + there are several precedents for such init() function
    names, e.g. amd_iommu_init_device(), free_area_init_node(),
    jump_label_init_type(), regmap_init_mmio_clk(),

  + It is not an argument but it was inconsistent even before.

Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 Documentation/RCU/lockdep-splat.txt         |  2 +-
 arch/x86/kvm/i8254.c                        | 14 +++++------
 crypto/crypto_engine.c                      | 16 ++++++-------
 drivers/block/loop.c                        |  8 +++----
 drivers/infiniband/sw/rdmavt/cq.c           | 10 ++++----
 drivers/md/dm.c                             | 10 ++++----
 drivers/media/pci/ivtv/ivtv-driver.c        |  6 ++---
 drivers/media/pci/ivtv/ivtv-irq.c           |  2 +-
 drivers/net/ethernet/microchip/encx24j600.c | 10 ++++----
 drivers/spi/spi.c                           | 18 +++++++-------
 drivers/tty/serial/sc16is7xx.c              | 22 ++++++++---------
 include/linux/kthread.h                     | 30 +++++++++++------------
 kernel/kthread.c                            | 37 +++++++++++++++--------------
 sound/soc/intel/baytrail/sst-baytrail-ipc.c |  2 +-
 sound/soc/intel/common/sst-ipc.c            |  6 ++---
 sound/soc/intel/haswell/sst-haswell-ipc.c   |  2 +-
 sound/soc/intel/skylake/skl-sst-ipc.c       |  2 +-
 17 files changed, 99 insertions(+), 98 deletions(-)

diff --git a/Documentation/RCU/lockdep-splat.txt b/Documentation/RCU/lockdep-splat.txt
index bf9061142827..238e9f61352f 100644
--- a/Documentation/RCU/lockdep-splat.txt
+++ b/Documentation/RCU/lockdep-splat.txt

@@ -57,7 +57,7 @@ Call Trace:
  [<ffffffff817db154>] kernel_thread_helper+0x4/0x10
  [<ffffffff81066430>] ? finish_task_switch+0x80/0x110
  [<ffffffff817d9c04>] ? retint_restore_args+0xe/0xe
- [<ffffffff81097510>] ? __init_kthread_worker+0x70/0x70
+ [<ffffffff81097510>] ? __kthread_init_worker+0x70/0x70
  [<ffffffff817db150>] ? gs_change+0xb/0xb
 
 Line 2776 of block/cfq-iosched.c in v3.0-rc5 is as follows:

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index a4bf5b45d65a..6e615e9459e5 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c

@@ -212,7 +212,7 @@ static void kvm_pit_ack_irq(struct kvm_irq_ack_notifier *kian)
 	 */
 	smp_mb();
 	if (atomic_dec_if_positive(&ps->pending) > 0)
-		queue_kthread_work(&pit->worker, &pit->expired);
+		kthread_queue_work(&pit->worker, &pit->expired);
 }
 
 void __kvm_migrate_pit_timer(struct kvm_vcpu *vcpu)

@@ -233,7 +233,7 @@ void __kvm_migrate_pit_timer(struct kvm_vcpu *vcpu)
 static void destroy_pit_timer(struct kvm_pit *pit)
 {
 	hrtimer_cancel(&pit->pit_state.timer);
-	flush_kthread_work(&pit->expired);
+	kthread_flush_work(&pit->expired);
 }
 
 static void pit_do_work(struct kthread_work *work)

@@ -272,7 +272,7 @@ static enum hrtimer_restart pit_timer_fn(struct hrtimer *data)
 	if (atomic_read(&ps->reinject))
 		atomic_inc(&ps->pending);
 
-	queue_kthread_work(&pt->worker, &pt->expired);
+	kthread_queue_work(&pt->worker, &pt->expired);
 
 	if (ps->is_periodic) {
 		hrtimer_add_expires_ns(&ps->timer, ps->period);

@@ -324,7 +324,7 @@ static void create_pit_timer(struct kvm_pit *pit, u32 val, int is_period)
 
 	/* TODO The new value only affected after the retriggered */
 	hrtimer_cancel(&ps->timer);
-	flush_kthread_work(&pit->expired);
+	kthread_flush_work(&pit->expired);
 	ps->period = interval;
 	ps->is_periodic = is_period;

@@ -668,13 +668,13 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
 	pid_nr = pid_vnr(pid);
 	put_pid(pid);
 
-	init_kthread_worker(&pit->worker);
+	kthread_init_worker(&pit->worker);
 	pit->worker_task = kthread_run(kthread_worker_fn, &pit->worker,
 				       "kvm-pit/%d", pid_nr);
 	if (IS_ERR(pit->worker_task))
 		goto fail_kthread;
 
-	init_kthread_work(&pit->expired, pit_do_work);
+	kthread_init_work(&pit->expired, pit_do_work);
 
 	pit->kvm = kvm;

@@ -728,7 +728,7 @@ void kvm_free_pit(struct kvm *kvm)
 		kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &pit->speaker_dev);
 		kvm_pit_set_reinject(pit, false);
 		hrtimer_cancel(&pit->pit_state.timer);
-		flush_kthread_work(&pit->expired);
+		kthread_flush_work(&pit->expired);
 		kthread_stop(pit->worker_task);
 		kvm_free_irq_source_id(kvm, pit->irq_source_id);
 		kfree(pit);

diff --git a/crypto/crypto_engine.c b/crypto/crypto_engine.c
index a55c82dd48ef..6bfcb2e1407f 100644
--- a/crypto/crypto_engine.c
+++ b/crypto/crypto_engine.c

@@ -47,7 +47,7 @@ static void crypto_pump_requests(struct crypto_engine *engine,
 
 	/* If another context is idling then defer */
 	if (engine->idling) {
-		queue_kthread_work(&engine->kworker, &engine->pump_requests);
+		kthread_queue_work(&engine->kworker, &engine->pump_requests);
 		goto out;
 	}

@@ -58,7 +58,7 @@ static void crypto_pump_requests(struct crypto_engine *engine,
 
 		/* Only do teardown in the thread */
 		if (!in_kthread) {
-			queue_kthread_work(&engine->kworker,
+			kthread_queue_work(&engine->kworker,
 					   &engine->pump_requests);
 			goto out;
 		}

@@ -157,7 +157,7 @@ int crypto_transfer_request(struct crypto_engine *engine,
 	ret = ablkcipher_enqueue_request(&engine->queue, req);
 
 	if (!engine->busy && need_pump)
-		queue_kthread_work(&engine->kworker, &engine->pump_requests);
+		kthread_queue_work(&engine->kworker, &engine->pump_requests);
 
 	spin_unlock_irqrestore(&engine->queue_lock, flags);
 	return ret;

@@ -210,7 +210,7 @@ void crypto_finalize_request(struct crypto_engine *engine,
 
 	req->base.complete(&req->base, err);
 
-	queue_kthread_work(&engine->kworker, &engine->pump_requests);
+	kthread_queue_work(&engine->kworker, &engine->pump_requests);
 }
 EXPORT_SYMBOL_GPL(crypto_finalize_request);

@@ -234,7 +234,7 @@ int crypto_engine_start(struct crypto_engine *engine)
 	engine->running = true;
 	spin_unlock_irqrestore(&engine->queue_lock, flags);
 
-	queue_kthread_work(&engine->kworker, &engine->pump_requests);
+	kthread_queue_work(&engine->kworker, &engine->pump_requests);
 
 	return 0;
 }

@@ -311,7 +311,7 @@ struct crypto_engine *crypto_engine_alloc_init(struct device *dev, bool rt)
 	crypto_init_queue(&engine->queue, CRYPTO_ENGINE_MAX_QLEN);
 	spin_lock_init(&engine->queue_lock);
 
-	init_kthread_worker(&engine->kworker);
+	kthread_init_worker(&engine->kworker);
 	engine->kworker_task = kthread_run(kthread_worker_fn,
 					   &engine->kworker, "%s",
 					   engine->name);

@@ -319,7 +319,7 @@ struct crypto_engine *crypto_engine_alloc_init(struct device *dev, bool rt)
 		dev_err(dev, "failed to create crypto request pump task\n");
 		return NULL;
 	}
-	init_kthread_work(&engine->pump_requests, crypto_pump_work);
+	kthread_init_work(&engine->pump_requests, crypto_pump_work);
 
 	if (engine->rt) {
 		dev_info(dev, "will run requests pump with realtime priority\n");

@@ -344,7 +344,7 @@ int crypto_engine_exit(struct crypto_engine *engine)
 	if (ret)
 		return ret;
 
-	flush_kthread_worker(&engine->kworker);
+	kthread_flush_worker(&engine->kworker);
 	kthread_stop(engine->kworker_task);
 
 	return 0;

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 1fa8cc235977..6e07125dbc07 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c

@@ -851,13 +851,13 @@ static void loop_config_discard(struct loop_device *lo)
 
 static void loop_unprepare_queue(struct loop_device *lo)
 {
-	flush_kthread_worker(&lo->worker);
+	kthread_flush_worker(&lo->worker);
 	kthread_stop(lo->worker_task);
 }
 
 static int loop_prepare_queue(struct loop_device *lo)
 {
-	init_kthread_worker(&lo->worker);
+	kthread_init_worker(&lo->worker);
 	lo->worker_task = kthread_run(kthread_worker_fn,
 			&lo->worker, "loop%d", lo->lo_number);
 	if (IS_ERR(lo->worker_task))

@@ -1665,7 +1665,7 @@ static int loop_queue_rq(struct blk_mq_hw_ctx *hctx,
 	else
 		cmd->use_aio = false;
 
-	queue_kthread_work(&lo->worker, &cmd->work);
+	kthread_queue_work(&lo->worker, &cmd->work);
 
 	return BLK_MQ_RQ_QUEUE_OK;
 }

@@ -1703,7 +1703,7 @@ static int loop_init_request(void *data, struct request *rq,
 	struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq);
 
 	cmd->rq = rq;
-	init_kthread_work(&cmd->work, loop_queue_work);
+	kthread_init_work(&cmd->work, loop_queue_work);
 
 	return 0;
 }

diff --git a/drivers/infiniband/sw/rdmavt/cq.c b/drivers/infiniband/sw/rdmavt/cq.c
index 6ca6fa80dd6e..4ae2b9928c5a 100644
--- a/drivers/infiniband/sw/rdmavt/cq.c
+++ b/drivers/infiniband/sw/rdmavt/cq.c

@@ -129,7 +129,7 @@ void rvt_cq_enter(struct rvt_cq *cq, struct ib_wc *entry, bool solicited)
 		if (likely(worker)) {
 			cq->notify = RVT_CQ_NONE;
 			cq->triggered++;
-			queue_kthread_work(worker, &cq->comptask);
+			kthread_queue_work(worker, &cq->comptask);
 		}
 	}

@@ -265,7 +265,7 @@ struct ib_cq *rvt_create_cq(struct ib_device *ibdev,
 	cq->ibcq.cqe = entries;
 	cq->notify = RVT_CQ_NONE;
 	spin_lock_init(&cq->lock);
-	init_kthread_work(&cq->comptask, send_complete);
+	kthread_init_work(&cq->comptask, send_complete);
 	cq->queue = wc;
 
 	ret = &cq->ibcq;

@@ -295,7 +295,7 @@ int rvt_destroy_cq(struct ib_cq *ibcq)
 	struct rvt_cq *cq = ibcq_to_rvtcq(ibcq);
 	struct rvt_dev_info *rdi = cq->rdi;
 
-	flush_kthread_work(&cq->comptask);
+	kthread_flush_work(&cq->comptask);
 	spin_lock(&rdi->n_cqs_lock);
 	rdi->n_cqs_allocated--;
 	spin_unlock(&rdi->n_cqs_lock);

@@ -513,7 +513,7 @@ int rvt_driver_cq_init(struct rvt_dev_info *rdi)
 	rdi->worker = kzalloc(sizeof(*rdi->worker), GFP_KERNEL);
 	if (!rdi->worker)
 		return -ENOMEM;
-	init_kthread_worker(rdi->worker);
+	kthread_init_worker(rdi->worker);
 	task = kthread_create_on_node(
 		kthread_worker_fn,
 		rdi->worker,

@@ -546,7 +546,7 @@ void rvt_cq_exit(struct rvt_dev_info *rdi)
 	/* blocks future queuing from send_complete() */
 	rdi->worker = NULL;
 	smp_wmb(); /* See rdi_cq_enter */
-	flush_kthread_worker(worker);
+	kthread_flush_worker(worker);
 	kthread_stop(worker->task);
 	kfree(worker);
 }

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 1b2f96205361..71b3a01866fb 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c

@@ -1937,7 +1937,7 @@ static void init_tio(struct dm_rq_target_io *tio, struct request *rq,
 	if (!md->init_tio_pdu)
 		memset(&tio->info, 0, sizeof(tio->info));
 	if (md->kworker_task)
-		init_kthread_work(&tio->work, map_tio_request);
+		kthread_init_work(&tio->work, map_tio_request);
 }
 
 static struct dm_rq_target_io *dm_old_prep_tio(struct request *rq,

@@ -2184,7 +2184,7 @@ static void dm_request_fn(struct request_queue *q)
 		tio = tio_from_request(rq);
 		/* Establish tio->ti before queuing work (map_tio_request) */
 		tio->ti = ti;
-		queue_kthread_work(&md->kworker, &tio->work);
+		kthread_queue_work(&md->kworker, &tio->work);
 		BUG_ON(!irqs_disabled());
 	}
 }

@@ -2657,7 +2657,7 @@ EXPORT_SYMBOL_GPL(dm_get_queue_limits);
 static void dm_old_init_rq_based_worker_thread(struct mapped_device *md)
 {
 	/* Initialize the request-based DM worker thread */
-	init_kthread_worker(&md->kworker);
+	kthread_init_worker(&md->kworker);
 	md->kworker_task = kthread_run(kthread_worker_fn, &md->kworker,
 				       "kdmwork-%s", dm_device_name(md));
 }

@@ -2930,7 +2930,7 @@ static void __dm_destroy(struct mapped_device *md, bool wait)
 	spin_unlock(&_minor_lock);
 
 	if (dm_request_based(md) && md->kworker_task)
-		flush_kthread_worker(&md->kworker);
+		kthread_flush_worker(&md->kworker);
 
 	/*
 	 * Take suspend_lock so that presuspend and postsuspend methods

@@ -3184,7 +3184,7 @@ static int __dm_suspend(struct mapped_device *md, struct dm_table *map,
 	if (dm_request_based(md)) {
 		dm_stop_queue(md->queue);
 		if (md->kworker_task)
-			flush_kthread_worker(&md->kworker);
+			kthread_flush_worker(&md->kworker);
 	}
 
 	flush_workqueue(md->wq);

diff --git a/drivers/media/pci/ivtv/ivtv-driver.c b/drivers/media/pci/ivtv/ivtv-driver.c
index 374033a5bdaf..ee48c3e09de4 100644
--- a/drivers/media/pci/ivtv/ivtv-driver.c
+++ b/drivers/media/pci/ivtv/ivtv-driver.c

@@ -750,7 +750,7 @@ static int ivtv_init_struct1(struct ivtv *itv)
 	spin_lock_init(&itv->lock);
 	spin_lock_init(&itv->dma_reg_lock);
 
-	init_kthread_worker(&itv->irq_worker);
+	kthread_init_worker(&itv->irq_worker);
 	itv->irq_worker_task = kthread_run(kthread_worker_fn, &itv->irq_worker,
 					   "%s", itv->v4l2_dev.name);
 	if (IS_ERR(itv->irq_worker_task)) {

@@ -760,7 +760,7 @@ static int ivtv_init_struct1(struct ivtv *itv)
 	/* must use the FIFO scheduler as it is realtime sensitive */
 	sched_setscheduler(itv->irq_worker_task, SCHED_FIFO, &param);
 
-	init_kthread_work(&itv->irq_work, ivtv_irq_work_handler);
+	kthread_init_work(&itv->irq_work, ivtv_irq_work_handler);
 
 	/* Initial settings */
 	itv->cxhdl.port = CX2341X_PORT_MEMORY;

@@ -1441,7 +1441,7 @@ static void ivtv_remove(struct pci_dev *pdev)
 	del_timer_sync(&itv->dma_timer);
 
 	/* Kill irq worker */
-	flush_kthread_worker(&itv->irq_worker);
+	kthread_flush_worker(&itv->irq_worker);
 	kthread_stop(itv->irq_worker_task);
 
 	ivtv_streams_cleanup(itv);

diff --git a/drivers/media/pci/ivtv/ivtv-irq.c b/drivers/media/pci/ivtv/ivtv-irq.c
index 36ca2d67c812..6efe1f71262c 100644
--- a/drivers/media/pci/ivtv/ivtv-irq.c
+++ b/drivers/media/pci/ivtv/ivtv-irq.c

@@ -1062,7 +1062,7 @@ irqreturn_t ivtv_irq_handler(int irq, void *dev_id)
 	}
 
 	if (test_and_clear_bit(IVTV_F_I_HAVE_WORK, &itv->i_flags)) {
-		queue_kthread_work(&itv->irq_worker, &itv->irq_work);
+		kthread_queue_work(&itv->irq_worker, &itv->irq_work);
 	}
 
 	spin_unlock(&itv->dma_reg_lock);

diff --git a/drivers/net/ethernet/microchip/encx24j600.c b/drivers/net/ethernet/microchip/encx24j600.c
index 42e34076d2de..b14f0305aa31 100644
--- a/drivers/net/ethernet/microchip/encx24j600.c
+++ b/drivers/net/ethernet/microchip/encx24j600.c

@@ -821,7 +821,7 @@ static void encx24j600_set_multicast_list(struct net_device *dev)
 	}
 
 	if (oldfilter != priv->rxfilter)
-		queue_kthread_work(&priv->kworker, &priv->setrx_work);
+		kthread_queue_work(&priv->kworker, &priv->setrx_work);
 }
 
 static void encx24j600_hw_tx(struct encx24j600_priv *priv)

@@ -879,7 +879,7 @@ static netdev_tx_t encx24j600_tx(struct sk_buff *skb, struct net_device *dev)
 	/* Remember the skb for deferred processing */
 	priv->tx_skb = skb;
 
-	queue_kthread_work(&priv->kworker, &priv->tx_work);
+	kthread_queue_work(&priv->kworker, &priv->tx_work);
 
 	return NETDEV_TX_OK;
 }

@@ -1037,9 +1037,9 @@ static int encx24j600_spi_probe(struct spi_device *spi)
 		goto out_free;
 	}
 
-	init_kthread_worker(&priv->kworker);
-	init_kthread_work(&priv->tx_work, encx24j600_tx_proc);
-	init_kthread_work(&priv->setrx_work, encx24j600_setrx_proc);
+	kthread_init_worker(&priv->kworker);
+	kthread_init_work(&priv->tx_work, encx24j600_tx_proc);
+	kthread_init_work(&priv->setrx_work, encx24j600_setrx_proc);
 
 	priv->kworker_task = kthread_run(kthread_worker_fn, &priv->kworker,
 					 "encx24j600");

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 77e6e45951f4..447e1f0bfb30 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c

@@ -1083,7 +1083,7 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread,
 
 	/* If another context is idling the device then defer */
 	if (master->idling) {
-		queue_kthread_work(&master->kworker, &master->pump_messages);
+		kthread_queue_work(&master->kworker, &master->pump_messages);
 		spin_unlock_irqrestore(&master->queue_lock, flags);
 		return;
 	}

@@ -1097,7 +1097,7 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread,
 
 		/* Only do teardown in the thread */
 		if (!in_kthread) {
-			queue_kthread_work(&master->kworker,
+			kthread_queue_work(&master->kworker,
 					   &master->pump_messages);
 			spin_unlock_irqrestore(&master->queue_lock, flags);
 			return;

@@ -1221,7 +1221,7 @@ static int spi_init_queue(struct spi_master *master)
 	master->running = false;
 	master->busy = false;
 
-	init_kthread_worker(&master->kworker);
+	kthread_init_worker(&master->kworker);
 	master->kworker_task = kthread_run(kthread_worker_fn,
 					   &master->kworker, "%s",
 					   dev_name(&master->dev));

@@ -1229,7 +1229,7 @@ static int spi_init_queue(struct spi_master *master)
 		dev_err(&master->dev, "failed to create message pump task\n");
 		return PTR_ERR(master->kworker_task);
 	}
-	init_kthread_work(&master->pump_messages, spi_pump_messages);
+	kthread_init_work(&master->pump_messages, spi_pump_messages);
 
 	/*
 	 * Master config will indicate if this controller should run the

@@ -1302,7 +1302,7 @@ void spi_finalize_current_message(struct spi_master *master)
 	spin_lock_irqsave(&master->queue_lock, flags);
 	master->cur_msg = NULL;
 	master->cur_msg_prepared = false;
-	queue_kthread_work(&master->kworker, &master->pump_messages);
+	kthread_queue_work(&master->kworker, &master->pump_messages);
 	spin_unlock_irqrestore(&master->queue_lock, flags);
 
 	trace_spi_message_done(mesg);

@@ -1328,7 +1328,7 @@ static int spi_start_queue(struct spi_master *master)
 	master->cur_msg = NULL;
 	spin_unlock_irqrestore(&master->queue_lock, flags);
 
-	queue_kthread_work(&master->kworker, &master->pump_messages);
+	kthread_queue_work(&master->kworker, &master->pump_messages);
 
 	return 0;
 }

@@ -1375,7 +1375,7 @@ static int spi_destroy_queue(struct spi_master *master)
 	ret = spi_stop_queue(master);
 
 	/*
-	 * flush_kthread_worker will block until all work is done.
+	 * kthread_flush_worker will block until all work is done.
 	 * If the reason that stop_queue timed out is that the work will never
 	 * finish, then it does no good to call flush/stop thread, so
 	 * return anyway.

@@ -1385,7 +1385,7 @@ static int spi_destroy_queue(struct spi_master *master)
 		return ret;
 	}
 
-	flush_kthread_worker(&master->kworker);
+	kthread_flush_worker(&master->kworker);
 	kthread_stop(master->kworker_task);
 
 	return 0;

@@ -1409,7 +1409,7 @@ static int __spi_queued_transfer(struct spi_device *spi,
 
 	list_add_tail(&msg->queue, &master->queue);
 	if (!master->busy && need_pump)
-		queue_kthread_work(&master->kworker, &master->pump_messages);
+		kthread_queue_work(&master->kworker, &master->pump_messages);
 
 	spin_unlock_irqrestore(&master->queue_lock, flags);
 	return 0;

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index f36e6df2fa90..1f6b9f641455 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c

@@ -708,7 +708,7 @@ static irqreturn_t sc16is7xx_irq(int irq, void *dev_id)
 {
 	struct sc16is7xx_port *s = (struct sc16is7xx_port *)dev_id;
 
-	queue_kthread_work(&s->kworker, &s->irq_work);
+	kthread_queue_work(&s->kworker, &s->irq_work);
 
 	return IRQ_HANDLED;
 }

@@ -784,7 +784,7 @@ static void sc16is7xx_ier_clear(struct uart_port *port, u8 bit)
 
 	one->config.flags |= SC16IS7XX_RECONF_IER;
 	one->config.ier_clear |= bit;
-	queue_kthread_work(&s->kworker, &one->reg_work);
+	kthread_queue_work(&s->kworker, &one->reg_work);
 }
 
 static void sc16is7xx_stop_tx(struct uart_port *port)

@@ -802,7 +802,7 @@ static void sc16is7xx_start_tx(struct uart_port *port)
 	struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
 	struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
 
-	queue_kthread_work(&s->kworker, &one->tx_work);
+	kthread_queue_work(&s->kworker, &one->tx_work);
 }
 
 static unsigned int sc16is7xx_tx_empty(struct uart_port *port)

@@ -828,7 +828,7 @@ static void sc16is7xx_set_mctrl(struct uart_port *port, unsigned int mctrl)
 	struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
 
 	one->config.flags |= SC16IS7XX_RECONF_MD;
-	queue_kthread_work(&s->kworker, &one->reg_work);
+	kthread_queue_work(&s->kworker, &one->reg_work);
 }
 
 static void sc16is7xx_break_ctl(struct uart_port *port, int break_state)

@@ -957,7 +957,7 @@ static int sc16is7xx_config_rs485(struct uart_port *port,
 
 	port->rs485 = *rs485;
 	one->config.flags |= SC16IS7XX_RECONF_RS485;
-	queue_kthread_work(&s->kworker, &one->reg_work);
+	kthread_queue_work(&s->kworker, &one->reg_work);
 
 	return 0;
 }

@@ -1030,7 +1030,7 @@ static void sc16is7xx_shutdown(struct uart_port *port)
 
 	sc16is7xx_power(port, 0);
 
-	flush_kthread_worker(&s->kworker);
+	kthread_flush_worker(&s->kworker);
 }
 
 static const char *sc16is7xx_type(struct uart_port *port)

@@ -1176,8 +1176,8 @@ static int sc16is7xx_probe(struct device *dev,
 	s->devtype = devtype;
 	dev_set_drvdata(dev, s);
 
-	init_kthread_worker(&s->kworker);
-	init_kthread_work(&s->irq_work, sc16is7xx_ist);
+	kthread_init_worker(&s->kworker);
+	kthread_init_work(&s->irq_work, sc16is7xx_ist);
 	s->kworker_task = kthread_run(kthread_worker_fn, &s->kworker,
 				      "sc16is7xx");
 	if (IS_ERR(s->kworker_task)) {

@@ -1230,8 +1230,8 @@ static int sc16is7xx_probe(struct device *dev,
 				     SC16IS7XX_EFCR_RXDISABLE_BIT |
 				     SC16IS7XX_EFCR_TXDISABLE_BIT);
 		/* Initialize kthread work structs */
-		init_kthread_work(&s->p[i].tx_work, sc16is7xx_tx_proc);
-		init_kthread_work(&s->p[i].reg_work, sc16is7xx_reg_proc);
+		kthread_init_work(&s->p[i].tx_work, sc16is7xx_tx_proc);
+		kthread_init_work(&s->p[i].reg_work, sc16is7xx_reg_proc);
 		/* Register port */
 		uart_add_one_port(&sc16is7xx_uart, &s->p[i].port);
 		/* Go to suspend mode */

@@ -1281,7 +1281,7 @@ static int sc16is7xx_remove(struct device *dev)
 		sc16is7xx_power(&s->p[i].port, 0);
 	}
 
-	flush_kthread_worker(&s->kworker);
+	kthread_flush_worker(&s->kworker);
 	kthread_stop(s->kworker_task);
 
 	if (!IS_ERR(s->clk))

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index c792ee1628d0..33d529a4c1dc 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h

@@ -57,7 +57,7 @@ extern int tsk_fork_get_node(struct task_struct *tsk);
  * Simple work processor based on kthread.
  *
  * This provides easier way to make use of kthreads.  A kthread_work
- * can be queued and flushed using queue/flush_kthread_work()
+ * can be queued and flushed using queue/kthread_flush_work()
  * respectively.  Queued kthread_works are processed by a kthread
  * running kthread_worker_fn().
  */

@@ -77,45 +77,45 @@ struct kthread_work {
 	struct kthread_worker	*worker;
 };
 
-#define KTHREAD_WORKER_INIT(worker)	{				\
+#define INIT_KTHREAD_WORKER(worker)	{				\
 	.lock = __SPIN_LOCK_UNLOCKED((worker).lock),			\
 	.work_list = LIST_HEAD_INIT((worker).work_list),		\
 	}
 
-#define KTHREAD_WORK_INIT(work, fn)	{				\
+#define INIT_KTHREAD_WORK(work, fn)	{				\
 	.node = LIST_HEAD_INIT((work).node),				\
 	.func = (fn),							\
 	}
 
 #define DEFINE_KTHREAD_WORKER(worker)					\
-	struct kthread_worker worker = KTHREAD_WORKER_INIT(worker)
+	struct kthread_worker worker = INIT_KTHREAD_WORKER(worker)
 
 #define DEFINE_KTHREAD_WORK(work, fn)					\
-	struct kthread_work work = KTHREAD_WORK_INIT(work, fn)
+	struct kthread_work work = INIT_KTHREAD_WORK(work, fn)
 
 /*
  * kthread_worker.lock needs its own lockdep class key when defined on
  * stack with lockdep enabled.  Use the following macros in such cases.
  */
 #ifdef CONFIG_LOCKDEP
-# define KTHREAD_WORKER_INIT_ONSTACK(worker)				\
-	({ init_kthread_worker(&worker); worker; })
+# define INIT_KTHREAD_WORKER_ONSTACK(worker)				\
+	({ kthread_init_worker(&worker); worker; })
 # define DEFINE_KTHREAD_WORKER_ONSTACK(worker)				\
-	struct kthread_worker worker = KTHREAD_WORKER_INIT_ONSTACK(worker)
+	struct kthread_worker worker = INIT_KTHREAD_WORKER_ONSTACK(worker)
 #else
 # define DEFINE_KTHREAD_WORKER_ONSTACK(worker) DEFINE_KTHREAD_WORKER(worker)
 #endif
 
-extern void __init_kthread_worker(struct kthread_worker *worker,
+extern void __kthread_init_worker(struct kthread_worker *worker,
 			const char *name, struct lock_class_key *key);
 
-#define init_kthread_worker(worker)					\
+#define kthread_init_worker(worker)					\
 	do {								\
 		static struct lock_class_key __key;			\
-		__init_kthread_worker((worker), "("#worker")->lock", &__key); \
+		__kthread_init_worker((worker), "("#worker")->lock", &__key); \
 	} while (0)
 
-#define init_kthread_work(work, fn)					\
+#define kthread_init_work(work, fn)					\
 	do {								\
 		memset((work), 0, sizeof(struct kthread_work));		\
 		INIT_LIST_HEAD(&(work)->node);				\

@@ -124,9 +124,9 @@ extern void __init_kthread_worker(struct kthread_worker *worker,
 
 int kthread_worker_fn(void *worker_ptr);
 
-bool queue_kthread_work(struct kthread_worker *worker,
+bool kthread_queue_work(struct kthread_worker *worker,
 			struct kthread_work *work);
-void flush_kthread_work(struct kthread_work *work);
-void flush_kthread_worker(struct kthread_worker *worker);
+void kthread_flush_work(struct kthread_work *work);
+void kthread_flush_worker(struct kthread_worker *worker);
 
 #endif /* _LINUX_KTHREAD_H */

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 0bec14aa844e..16cea43c3c2c 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c

@@ -536,7 +536,7 @@ int kthreadd(void *unused)
 	return 0;
 }
 
-void __init_kthread_worker(struct kthread_worker *worker,
+void __kthread_init_worker(struct kthread_worker *worker,
 				const char *name,
 				struct lock_class_key *key)
 {

@@ -545,7 +545,7 @@ void __init_kthread_worker(struct kthread_worker *worker,
 	INIT_LIST_HEAD(&worker->work_list);
 	worker->task = NULL;
 }
-EXPORT_SYMBOL_GPL(__init_kthread_worker);
+EXPORT_SYMBOL_GPL(__kthread_init_worker);
 
 /**
  * kthread_worker_fn - kthread function to process kthread_worker

@@ -602,7 +602,7 @@ repeat:
 EXPORT_SYMBOL_GPL(kthread_worker_fn);
 
 /* insert @work before @pos in @worker */
-static void insert_kthread_work(struct kthread_worker *worker,
+static void kthread_insert_work(struct kthread_worker *worker,
 			       struct kthread_work *work,
 			       struct list_head *pos)
 {

@@ -615,7 +615,7 @@ static void insert_kthread_work(struct kthread_worker *worker,
 }
 
 /**
- * queue_kthread_work - queue a kthread_work
+ * kthread_queue_work - queue a kthread_work
  * @worker: target kthread_worker
  * @work: kthread_work to queue
  *

@@ -623,7 +623,7 @@ static void insert_kthread_work(struct kthread_worker *worker,
  * must have been created with kthread_worker_create().  Returns %true
  * if @work was successfully queued, %false if it was already pending.
  */
-bool queue_kthread_work(struct kthread_worker *worker,
+bool kthread_queue_work(struct kthread_worker *worker,
 			struct kthread_work *work)
 {
 	bool ret = false;

@@ -631,13 +631,13 @@ bool queue_kthread_work(struct kthread_worker *worker,
 
 	spin_lock_irqsave(&worker->lock, flags);
 	if (list_empty(&work->node)) {
-		insert_kthread_work(worker, work, &worker->work_list);
+		kthread_insert_work(worker, work, &worker->work_list);
 		ret = true;
 	}
 	spin_unlock_irqrestore(&worker->lock, flags);
 	return ret;
 }
-EXPORT_SYMBOL_GPL(queue_kthread_work);
+EXPORT_SYMBOL_GPL(kthread_queue_work);
 
 struct kthread_flush_work {
 	struct kthread_work	work;

@@ -652,15 +652,15 @@ static void kthread_flush_work_fn(struct kthread_work *work)
 }
 
 /**
- * flush_kthread_work - flush a kthread_work
+ * kthread_flush_work - flush a kthread_work
  * @work: work to flush
  *
  * If @work is queued or executing, wait for it to finish execution.
  */
-void flush_kthread_work(struct kthread_work *work)
+void kthread_flush_work(struct kthread_work *work)
 {
 	struct kthread_flush_work fwork = {
-		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
+		INIT_KTHREAD_WORK(fwork.work, kthread_flush_work_fn),
 		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
 	};
 	struct kthread_worker *worker;

@@ -678,9 +678,10 @@ retry:
 	}
 
 	if (!list_empty(&work->node))
-		insert_kthread_work(worker, &fwork.work, work->node.next);
+		kthread_insert_work(worker, &fwork.work, work->node.next);
 	else if (worker->current_work == work)
-		insert_kthread_work(worker, &fwork.work, worker->work_list.next);
+		kthread_insert_work(worker, &fwork.work,
+				    worker->work_list.next);
 	else
 		noop = true;

@@ -689,23 +690,23 @@ retry:
 	if (!noop)
 		wait_for_completion(&fwork.done);
 }
-EXPORT_SYMBOL_GPL(flush_kthread_work);
+EXPORT_SYMBOL_GPL(kthread_flush_work);
 
 /**
- * flush_kthread_worker - flush all current works on a kthread_worker
+ * kthread_flush_worker - flush all current works on a kthread_worker
  * @worker: worker to flush
  *
  * Wait until all currently executing or pending works on @worker are
  * finished.
  */
-void flush_kthread_worker(struct kthread_worker *worker)
+void kthread_flush_worker(struct kthread_worker *worker)
 {
 	struct kthread_flush_work fwork = {
-		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
+		INIT_KTHREAD_WORK(fwork.work, kthread_flush_work_fn),
 		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
 	};
 
-	queue_kthread_work(worker, &fwork.work);
+	kthread_queue_work(worker, &fwork.work);
 	wait_for_completion(&fwork.done);
 }
-EXPORT_SYMBOL_GPL(flush_kthread_worker);
+EXPORT_SYMBOL_GPL(kthread_flush_worker);

diff --git a/sound/soc/intel/baytrail/sst-baytrail-ipc.c b/sound/soc/intel/baytrail/sst-baytrail-ipc.c
index 5bbaa667bec1..c66a5ec18182 100644
--- a/sound/soc/intel/baytrail/sst-baytrail-ipc.c
+++ b/sound/soc/intel/baytrail/sst-baytrail-ipc.c

@@ -344,7 +344,7 @@ static irqreturn_t sst_byt_irq_thread(int irq, void *context)
 	spin_unlock_irqrestore(&sst->spinlock, flags);
 
 	/* continue to send any remaining messages... */
-	queue_kthread_work(&ipc->kworker, &ipc->kwork);
+	kthread_queue_work(&ipc->kworker, &ipc->kwork);
 
 	return IRQ_HANDLED;
 }

diff --git a/sound/soc/intel/common/sst-ipc.c b/sound/soc/intel/common/sst-ipc.c
index a12c7bb08d3b..6c672ac79cce 100644
--- a/sound/soc/intel/common/sst-ipc.c
+++ b/sound/soc/intel/common/sst-ipc.c

@@ -111,7 +111,7 @@ static int ipc_tx_message(struct sst_generic_ipc *ipc, u64 header,
 	list_add_tail(&msg->list, &ipc->tx_list);
 	spin_unlock_irqrestore(&ipc->dsp->spinlock, flags);
 
-	queue_kthread_work(&ipc->kworker, &ipc->kwork);
+	kthread_queue_work(&ipc->kworker, &ipc->kwork);
 
 	if (wait)
 		return tx_wait_done(ipc, msg, rx_data);

@@ -281,7 +281,7 @@ int sst_ipc_init(struct sst_generic_ipc *ipc)
 		return -ENOMEM;
 
 	/* start the IPC message thread */
-	init_kthread_worker(&ipc->kworker);
+	kthread_init_worker(&ipc->kworker);
 	ipc->tx_thread = kthread_run(kthread_worker_fn,
 					&ipc->kworker, "%s",
 					dev_name(ipc->dev));

@@ -292,7 +292,7 @@ int sst_ipc_init(struct sst_generic_ipc *ipc)
 		return ret;
 	}
 
-	init_kthread_work(&ipc->kwork, ipc_tx_msgs);
+	kthread_init_work(&ipc->kwork, ipc_tx_msgs);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(sst_ipc_init);

diff --git a/sound/soc/intel/haswell/sst-haswell-ipc.c b/sound/soc/intel/haswell/sst-haswell-ipc.c
index 91565229d074..e432a31fd9f2 100644
--- a/sound/soc/intel/haswell/sst-haswell-ipc.c
+++ b/sound/soc/intel/haswell/sst-haswell-ipc.c

@@ -818,7 +818,7 @@ static irqreturn_t hsw_irq_thread(int irq, void *context)
 	spin_unlock_irqrestore(&sst->spinlock, flags);
 
 	/* continue to send any remaining messages... */
-	queue_kthread_work(&ipc->kworker, &ipc->kwork);
+	kthread_queue_work(&ipc->kworker, &ipc->kwork);
 
 	return IRQ_HANDLED;
 }

diff --git a/sound/soc/intel/skylake/skl-sst-ipc.c b/sound/soc/intel/skylake/skl-sst-ipc.c
index 543460293b00..2790f3457eb6 100644
--- a/sound/soc/intel/skylake/skl-sst-ipc.c
+++ b/sound/soc/intel/skylake/skl-sst-ipc.c

@@ -458,7 +458,7 @@ irqreturn_t skl_dsp_irq_thread_handler(int irq, void *context)
 	skl_ipc_int_enable(dsp);
 
 	/* continue to send any remaining messages... */
-	queue_kthread_work(&ipc->kworker, &ipc->kwork);
+	kthread_queue_work(&ipc->kworker, &ipc->kwork);
 
 	return IRQ_HANDLED;
 }

-- 
1.8.5.6

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[PATCH v9 03/12] kthread/smpboot: Do not park in kthread_create_on_cpu()

From: Petr Mladek <pmladek@suse.com>
Date: 2016-06-16 11:18:05

kthread_create_on_cpu() was added by the commit 2a1d446019f9a5983e
("kthread: Implement park/unpark facility"). It is currently used
only when enabling new CPU. For this purpose, the newly created
kthread has to be parked.

The CPU binding is a bit tricky. The kthread is parked when the CPU
has not been allowed yet. And the CPU is bound when the kthread
is unparked.

The function would be useful for more per-CPU kthreads, e.g.
bnx2fc_thread, fcoethread. For this purpose, the newly created
kthread should stay in the uninterruptible state.

This patch moves the parking into smpboot. It binds the thread
already when created. Then the function might be used universally.
Also the behavior is consistent with kthread_create() and
kthread_create_on_node().

Signed-off-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Thomas Gleixner <redacted>
---
 kernel/kthread.c | 8 ++++++--
 kernel/smpboot.c | 5 +++++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 16cea43c3c2c..aea12c9fec98 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c

@@ -390,10 +390,10 @@ struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
 				   cpu);
 	if (IS_ERR(p))
 		return p;
+	kthread_bind(p, cpu);
+	/* CPU hotplug need to bind once again when unparking the thread. */
 	set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags);
 	to_kthread(p)->cpu = cpu;
-	/* Park the thread to get it out of TASK_UNINTERRUPTIBLE state */
-	kthread_park(p);
 	return p;
 }

@@ -407,6 +407,10 @@ static void __kthread_unpark(struct task_struct *k, struct kthread *kthread)
 	 * which might be about to be cleared.
 	 */
 	if (test_and_clear_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
+		/*
+		 * Newly created kthread was parked when the CPU was offline.
+		 * The binding was lost and we need to set it again.
+		 */
 		if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
 			__kthread_bind(k, kthread->cpu, TASK_PARKED);
 		wake_up_state(k, TASK_PARKED);

diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index 13bc43d1fb22..4a5c6e73ecd4 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c

@@ -186,6 +186,11 @@ __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
 		kfree(td);
 		return PTR_ERR(tsk);
 	}
+	/*
+	 * Park the thread so that it could start right on the CPU
+	 * when it is available.
+	 */
+	kthread_park(tsk);
 	get_task_struct(tsk);
 	*per_cpu_ptr(ht->store, cpu) = tsk;
 	if (ht->create) {

-- 
1.8.5.6

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[PATCH v9 04/12] kthread: Allow to call __kthread_create_on_node() with va_list args

From: Petr Mladek <pmladek@suse.com>
Date: 2016-06-16 11:18:13

kthread_create_on_node() implements a bunch of logic to create
the kthread. It is already called by kthread_create_on_cpu().

We are going to extend the kthread worker API and will
need to call kthread_create_on_node() with va_list args there.

This patch does only a refactoring and does not modify the existing
behavior.

Signed-off-by: Petr Mladek <pmladek-IBi9RG/b67k@public.gmane.org>
---
 kernel/kthread.c | 72 +++++++++++++++++++++++++++++++++-----------------------
 1 file changed, 42 insertions(+), 30 deletions(-)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index aea12c9fec98..8ed2a4434185 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c

@@ -244,33 +244,10 @@ static void create_kthread(struct kthread_create_info *create)
 	}
 }
 
-/**
- * kthread_create_on_node - create a kthread.
- * @threadfn: the function to run until signal_pending(current).
- * @data: data ptr for @threadfn.
- * @node: task and thread structures for the thread are allocated on this node
- * @namefmt: printf-style name for the thread.
- *
- * Description: This helper function creates and names a kernel
- * thread.  The thread will be stopped: use wake_up_process() to start
- * it.  See also kthread_run().  The new thread has SCHED_NORMAL policy and
- * is affine to all CPUs.
- *
- * If thread is going to be bound on a particular cpu, give its node
- * in @node, to get NUMA affinity for kthread stack, or else give NUMA_NO_NODE.
- * When woken, the thread will run @threadfn() with @data as its
- * argument. @threadfn() can either call do_exit() directly if it is a
- * standalone thread for which no one will call kthread_stop(), or
- * return when 'kthread_should_stop()' is true (which means
- * kthread_stop() has been called).  The return value should be zero
- * or a negative error number; it will be passed to kthread_stop().
- *
- * Returns a task_struct or ERR_PTR(-ENOMEM) or ERR_PTR(-EINTR).
- */
-struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
-					   void *data, int node,
-					   const char namefmt[],
-					   ...)
+static struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
+						    void *data, int node,
+						    const char namefmt[],
+						    va_list args)
 {
 	DECLARE_COMPLETION_ONSTACK(done);
 	struct task_struct *task;

@@ -311,11 +288,8 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
 	task = create->result;
 	if (!IS_ERR(task)) {
 		static const struct sched_param param = { .sched_priority = 0 };
-		va_list args;
 
-		va_start(args, namefmt);
 		vsnprintf(task->comm, sizeof(task->comm), namefmt, args);
-		va_end(args);
 		/*
 		 * root may have changed our (kthreadd's) priority or CPU mask.
 		 * The kernel thread should not inherit these properties.

@@ -326,6 +300,44 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
 	kfree(create);
 	return task;
 }
+
+/**
+ * kthread_create_on_node - create a kthread.
+ * @threadfn: the function to run until signal_pending(current).
+ * @data: data ptr for @threadfn.
+ * @node: task and thread structures for the thread are allocated on this node
+ * @namefmt: printf-style name for the thread.
+ *
+ * Description: This helper function creates and names a kernel
+ * thread.  The thread will be stopped: use wake_up_process() to start
+ * it.  See also kthread_run().  The new thread has SCHED_NORMAL policy and
+ * is affine to all CPUs.
+ *
+ * If thread is going to be bound on a particular cpu, give its node
+ * in @node, to get NUMA affinity for kthread stack, or else give NUMA_NO_NODE.
+ * When woken, the thread will run @threadfn() with @data as its
+ * argument. @threadfn() can either call do_exit() directly if it is a
+ * standalone thread for which no one will call kthread_stop(), or
+ * return when 'kthread_should_stop()' is true (which means
+ * kthread_stop() has been called).  The return value should be zero
+ * or a negative error number; it will be passed to kthread_stop().
+ *
+ * Returns a task_struct or ERR_PTR(-ENOMEM) or ERR_PTR(-EINTR).
+ */
+struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
+					   void *data, int node,
+					   const char namefmt[],
+					   ...)
+{
+	struct task_struct *task;
+	va_list args;
+
+	va_start(args, namefmt);
+	task = __kthread_create_on_node(threadfn, data, node, namefmt, args);
+	va_end(args);
+
+	return task;
+}
 EXPORT_SYMBOL(kthread_create_on_node);
 
 static void __kthread_bind_mask(struct task_struct *p, const struct cpumask *mask, long state)

-- 
1.8.5.6

[PATCH v9 05/12] kthread: Add kthread_create_worker*()

From: Petr Mladek <pmladek@suse.com>
Date: 2016-06-16 11:18:55

Kthread workers are currently created using the classic kthread API,
namely kthread_run(). kthread_worker_fn() is passed as the @threadfn
parameter.

This patch defines kthread_create_worker() and
kthread_create_worker_on_cpu() functions that hide implementation details.

They enforce using kthread_worker_fn() for the main thread. But I doubt
that there are any plans to create any alternative. In fact, I think
that we do not want any alternative main thread because it would be
hard to support consistency with the rest of the kthread worker API.

The naming and function of kthread_create_worker() is inspired by
the workqueues API like the rest of the kthread worker API.

The kthread_create_worker_on_cpu() variant is motivated by the original
kthread_create_on_cpu(). Note that we need to bind per-CPU kthread
workers already when they are created. It makes the life easier.
kthread_bind() could not be used later for an already running worker.

This patch does _not_ convert existing kthread workers. The kthread worker
API need more improvements first, e.g. a function to destroy the worker.

IMPORTANT:

kthread_create_worker_on_cpu() allows to use any format of the
worker name, in compare with kthread_create_on_cpu(). The good thing
is that it is more generic. The bad thing is that most users will
need to pass the cpu number in two parameters, e.g.
kthread_create_worker_on_cpu(cpu, "helper/%d", cpu).

To be honest, the main motivation was to avoid the need for an
empty va_list. The only legal way was to create a helper function that
would be called with an empty list. Other attempts caused compilation
warnings or even errors on different architectures.

There were also other alternatives, for example, using #define or
splitting __kthread_create_worker(). The used solution looked
like the least ugly.

Signed-off-by: Petr Mladek <pmladek-IBi9RG/b67k@public.gmane.org>
---
 include/linux/kthread.h |   7 +++
 kernel/kthread.c        | 113 +++++++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 110 insertions(+), 10 deletions(-)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 33d529a4c1dc..f68041837dd6 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h

@@ -124,6 +124,13 @@ extern void __kthread_init_worker(struct kthread_worker *worker,
 
 int kthread_worker_fn(void *worker_ptr);
 
+__printf(1, 2)
+struct kthread_worker *
+kthread_create_worker(const char namefmt[], ...);
+
+struct kthread_worker *
+kthread_create_worker_on_cpu(int cpu, const char namefmt[], ...);
+
 bool kthread_queue_work(struct kthread_worker *worker,
 			struct kthread_work *work);
 void kthread_flush_work(struct kthread_work *work);

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 8ed2a4434185..590b9f699e9d 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c

@@ -567,23 +567,24 @@ EXPORT_SYMBOL_GPL(__kthread_init_worker);
  * kthread_worker_fn - kthread function to process kthread_worker
  * @worker_ptr: pointer to initialized kthread_worker
  *
- * This function can be used as @threadfn to kthread_create() or
- * kthread_run() with @worker_ptr argument pointing to an initialized
- * kthread_worker.  The started kthread will process work_list until
- * the it is stopped with kthread_stop().  A kthread can also call
- * this function directly after extra initialization.
+ * This function implements the main cycle of kthread worker. It processes
+ * work_list until it is stopped with kthread_stop(). It sleeps when the queue
+ * is empty.
  *
- * Different kthreads can be used for the same kthread_worker as long
- * as there's only one kthread attached to it at any given time.  A
- * kthread_worker without an attached kthread simply collects queued
- * kthread_works.
+ * The works are not allowed to keep any locks, disable preemption or interrupts
+ * when they finish. There is defined a safe point for freezing when one work
+ * finishes and before a new one is started.
  */
 int kthread_worker_fn(void *worker_ptr)
 {
 	struct kthread_worker *worker = worker_ptr;
 	struct kthread_work *work;
 
-	WARN_ON(worker->task);
+	/*
+	 * FIXME: Update the check and remove the assignment when all kthread
+	 * worker users are created using kthread_create_worker*() functions.
+	 */
+	WARN_ON(worker->task && worker->task != current);
 	worker->task = current;
 repeat:
 	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */

@@ -617,6 +618,98 @@ repeat:
 }
 EXPORT_SYMBOL_GPL(kthread_worker_fn);
 
+static struct kthread_worker *
+__kthread_create_worker(int cpu, const char namefmt[], va_list args)
+{
+	struct kthread_worker *worker;
+	struct task_struct *task;
+
+	worker = kzalloc(sizeof(*worker), GFP_KERNEL);
+	if (!worker)
+		return ERR_PTR(-ENOMEM);
+
+	kthread_init_worker(worker);
+
+	if (cpu >= 0) {
+		char name[TASK_COMM_LEN];
+
+		/*
+		 * kthread_create_worker_on_cpu() allows to pass a generic
+		 * namefmt in compare with kthread_create_on_cpu. We need
+		 * to format it here.
+		 */
+		vsnprintf(name, sizeof(name), namefmt, args);
+		task = kthread_create_on_cpu(kthread_worker_fn, worker,
+					     cpu, name);
+	} else {
+		task = __kthread_create_on_node(kthread_worker_fn, worker,
+						-1, namefmt, args);
+	}
+
+	if (IS_ERR(task))
+		goto fail_task;
+
+	worker->task = task;
+	wake_up_process(task);
+	return worker;
+
+fail_task:
+	kfree(worker);
+	return ERR_CAST(task);
+}
+
+/**
+ * kthread_create_worker - create a kthread worker
+ * @namefmt: printf-style name for the kthread worker (task).
+ *
+ * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
+ * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
+ * when the worker was SIGKILLed.
+ */
+struct kthread_worker *
+kthread_create_worker(const char namefmt[], ...)
+{
+	struct kthread_worker *worker;
+	va_list args;
+
+	va_start(args, namefmt);
+	worker = __kthread_create_worker(-1, namefmt, args);
+	va_end(args);
+
+	return worker;
+}
+EXPORT_SYMBOL(kthread_create_worker);
+
+/**
+ * kthread_create_worker_on_cpu - create a kthread worker and bind it
+ *	it to a given CPU and the associated NUMA node.
+ * @cpu: CPU number
+ * @namefmt: printf-style name for the kthread worker (task).
+ *
+ * Use a valid CPU number if you want to bind the kthread worker
+ * to the given CPU and the associated NUMA node.
+ *
+ * A good practice is to add the cpu number also into the worker name.
+ * For example, use kthread_create_worker_on_cpu(cpu, "helper/%d", cpu).
+ *
+ * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
+ * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
+ * when the worker was SIGKILLed.
+ */
+struct kthread_worker *
+kthread_create_worker_on_cpu(int cpu, const char namefmt[], ...)
+{
+	struct kthread_worker *worker;
+	va_list args;
+
+	va_start(args, namefmt);
+	worker = __kthread_create_worker(cpu, namefmt, args);
+	va_end(args);
+
+	return worker;
+}
+EXPORT_SYMBOL(kthread_create_worker_on_cpu);
+
 /* insert @work before @pos in @worker */
 static void kthread_insert_work(struct kthread_worker *worker,
 			       struct kthread_work *work,

-- 
1.8.5.6

[PATCH v9 06/12] kthread: Add kthread_drain_worker()

From: Petr Mladek <pmladek@suse.com>
Date: 2016-06-16 11:19:05

kthread_flush_worker() returns when the currently queued works are proceed.
But some other works might have been queued in the meantime.

This patch adds kthread_drain_worker() that is inspired by
drain_workqueue(). It returns when the queue is completely
empty and warns when it takes too long.

The initial implementation does not block queuing new works when
draining. It makes things much easier. The blocking would be useful
to debug potential problems but it is not clear if it is worth
the complication at the moment.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 include/linux/kthread.h |  1 +
 kernel/kthread.c        | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index f68041837dd6..c889b653f8cb 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h

@@ -135,5 +135,6 @@ bool kthread_queue_work(struct kthread_worker *worker,
 			struct kthread_work *work);
 void kthread_flush_work(struct kthread_work *work);
 void kthread_flush_worker(struct kthread_worker *worker);
+void kthread_drain_worker(struct kthread_worker *worker);
 
 #endif /* _LINUX_KTHREAD_H */

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 590b9f699e9d..4454b1267718 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c

@@ -819,3 +819,37 @@ void kthread_flush_worker(struct kthread_worker *worker)
 	wait_for_completion(&fwork.done);
 }
 EXPORT_SYMBOL_GPL(kthread_flush_worker);
+
+/**
+ * kthread_drain_worker - drain a kthread worker
+ * @worker: worker to be drained
+ *
+ * Wait until there is no work queued for the given kthread worker.
+ * @worker is flushed repeatedly until it becomes empty.  The number
+ * of flushing is determined by the depth of chaining and should
+ * be relatively short.  Whine if it takes too long.
+ *
+ * The caller is responsible for blocking all users of this kthread
+ * worker from queuing new works. Also it is responsible for blocking
+ * the already queued works from an infinite re-queuing!
+ */
+void kthread_drain_worker(struct kthread_worker *worker)
+{
+	int flush_cnt = 0;
+
+	spin_lock_irq(&worker->lock);
+
+	while (!list_empty(&worker->work_list)) {
+		spin_unlock_irq(&worker->lock);
+
+		kthread_flush_worker(worker);
+		WARN_ONCE(flush_cnt++ > 10,
+			  "kthread worker %s: kthread_drain_worker() isn't complete after %u tries\n",
+			  worker->task->comm, flush_cnt);
+
+		spin_lock_irq(&worker->lock);
+	}
+
+	spin_unlock_irq(&worker->lock);
+}
+EXPORT_SYMBOL(kthread_drain_worker);

-- 
1.8.5.6

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[PATCH v9 07/12] kthread: Add kthread_destroy_worker()

From: Petr Mladek <pmladek@suse.com>
Date: 2016-06-16 11:19:12

The current kthread worker users call flush() and stop() explicitly.
This function drains the worker, stops it, and frees the kthread_worker
struct in one call.

It is supposed to be used together with kthread_create_worker*() that
allocates struct kthread_worker.

Also note that drain() correctly handles self-queuing works in compare
with flush().

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 include/linux/kthread.h |  2 ++
 kernel/kthread.c        | 21 +++++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index c889b653f8cb..b2c4dcea8f51 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h

@@ -137,4 +137,6 @@ void kthread_flush_work(struct kthread_work *work);
 void kthread_flush_worker(struct kthread_worker *worker);
 void kthread_drain_worker(struct kthread_worker *worker);
 
+void kthread_destroy_worker(struct kthread_worker *worker);
+
 #endif /* _LINUX_KTHREAD_H */

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 4454b1267718..567ec49b4872 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c

@@ -853,3 +853,24 @@ void kthread_drain_worker(struct kthread_worker *worker)
 	spin_unlock_irq(&worker->lock);
 }
 EXPORT_SYMBOL(kthread_drain_worker);
+
+/**
+ * kthread_destroy_worker - destroy a kthread worker
+ * @worker: worker to be destroyed
+ *
+ * Drain and destroy @worker.  It has the same conditions
+ * for use as kthread_drain_worker(), see above.
+ */
+void kthread_destroy_worker(struct kthread_worker *worker)
+{
+	struct task_struct *task;
+
+	task = worker->task;
+	if (WARN_ON(!task))
+		return;
+
+	kthread_drain_worker(worker);
+	kthread_stop(task);
+	kfree(worker);
+}
+EXPORT_SYMBOL(kthread_destroy_worker);

-- 
1.8.5.6

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[PATCH v9 08/12] kthread: Detect when a kthread work is used by more workers

From: Petr Mladek <pmladek@suse.com>
Date: 2016-06-16 11:19:21

Nothing currently prevents a work from queuing for a kthread worker
when it is already running on another one. This means that the work
might run in parallel on more workers. Also some operations, e.g.
flush or drain are not reliable.

This problem will be even more visible after we add kthread_cancel_work()
function. It will only have "work" as the parameter and will use
worker->lock to synchronize with others.

Well, normally this is not a problem because the API users are sane.
But bugs might happen and users also might be crazy.

This patch adds a warning when we try to insert the work for another
worker. It does not fully prevent the misuse because it would make the
code much more complicated without a big benefit.

It adds the same warning also into kthread_flush_work() instead of
the repeated attempts to get the right lock.

A side effect is that one needs to explicitly reinitialize the work
if it must be queued into another worker. This is needed, for example,
when the worker is stopped and started again. It is a bit inconvenient.
But it looks like a good compromise between the stability and complexity.

I have double checked all existing users of the kthread worker API
and they all seems to initialize the work after the worker gets
started.

Just for completeness, the patch adds a check that the work is not
already in a queue.

The patch also puts all the checks into a separate function. It will
be reused when implementing delayed works.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 kernel/kthread.c | 28 ++++++++++++++++++++--------
 1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 567ec49b4872..8e9548649c86 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c

@@ -574,6 +574,9 @@ EXPORT_SYMBOL_GPL(__kthread_init_worker);
  * The works are not allowed to keep any locks, disable preemption or interrupts
  * when they finish. There is defined a safe point for freezing when one work
  * finishes and before a new one is started.
+ *
+ * Also the works must not be handled by more workers at the same time, see also
+ * kthread_queue_work().
  */
 int kthread_worker_fn(void *worker_ptr)
 {

@@ -710,12 +713,21 @@ kthread_create_worker_on_cpu(int cpu, const char namefmt[], ...)
 }
 EXPORT_SYMBOL(kthread_create_worker_on_cpu);
 
+static void kthread_insert_work_sanity_check(struct kthread_worker *worker,
+					     struct kthread_work *work)
+{
+	lockdep_assert_held(&worker->lock);
+	WARN_ON_ONCE(!list_empty(&work->node));
+	/* Do not use a work with more workers, see kthread_queue_work() */
+	WARN_ON_ONCE(work->worker && work->worker != worker);
+}
+
 /* insert @work before @pos in @worker */
 static void kthread_insert_work(struct kthread_worker *worker,
-			       struct kthread_work *work,
-			       struct list_head *pos)
+				struct kthread_work *work,
+				struct list_head *pos)
 {
-	lockdep_assert_held(&worker->lock);
+	kthread_insert_work_sanity_check(worker, work);
 
 	list_add_tail(&work->node, pos);
 	work->worker = worker;

@@ -731,6 +743,9 @@ static void kthread_insert_work(struct kthread_worker *worker,
  * Queue @work to work processor @task for async execution.  @task
  * must have been created with kthread_worker_create().  Returns %true
  * if @work was successfully queued, %false if it was already pending.
+ *
+ * Reinitialize the work if it needs to be used by another worker.
+ * For example, when the worker was stopped and started again.
  */
 bool kthread_queue_work(struct kthread_worker *worker,
 			struct kthread_work *work)

@@ -775,16 +790,13 @@ void kthread_flush_work(struct kthread_work *work)
 	struct kthread_worker *worker;
 	bool noop = false;
 
-retry:
 	worker = work->worker;
 	if (!worker)
 		return;
 
 	spin_lock_irq(&worker->lock);
-	if (work->worker != worker) {
-		spin_unlock_irq(&worker->lock);
-		goto retry;
-	}
+	/* Work must not be used with more workers, see kthread_queue_work(). */
+	WARN_ON_ONCE(work->worker != worker);
 
 	if (!list_empty(&work->node))
 		kthread_insert_work(worker, &fwork.work, work->node.next);

-- 
1.8.5.6

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[PATCH v9 09/12] kthread: Initial support for delayed kthread work

From: Petr Mladek <pmladek@suse.com>
Date: 2016-06-16 11:19:36

We are going to use kthread_worker more widely and delayed works
will be pretty useful.

The implementation is inspired by workqueues. It uses a timer to
queue the work after the requested delay. If the delay is zero,
the work is queued immediately.

In compare with workqueues, each work is associated with a single
worker (kthread). Therefore the implementation could be much easier.
In particular, we use the worker->lock to synchronize all the
operations with the work. We do not need any atomic operation
with a flags variable.

In fact, we do not need any state variable at all. Instead, we
add a list of delayed works into the worker. Then the pending
work is listed either in the list of queued or delayed works.
And the existing check of pending works is the same even for
the delayed ones.

A work must not be assigned to another worker unless reinitialized.
Therefore the timer handler might expect that dwork->work->worker
is valid and it could simply take the lock. We just add some
sanity checks to help with debugging a potential misuse.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 include/linux/kthread.h |  33 ++++++++++++++++
 kernel/kthread.c        | 102 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 135 insertions(+)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index b2c4dcea8f51..98d167187013 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h

@@ -63,10 +63,12 @@ extern int tsk_fork_get_node(struct task_struct *tsk);
  */
 struct kthread_work;
 typedef void (*kthread_work_func_t)(struct kthread_work *work);
+void kthread_delayed_work_timer_fn(unsigned long __data);
 
 struct kthread_worker {
 	spinlock_t		lock;
 	struct list_head	work_list;
+	struct list_head	delayed_work_list;
 	struct task_struct	*task;
 	struct kthread_work	*current_work;
 };

@@ -77,9 +79,15 @@ struct kthread_work {
 	struct kthread_worker	*worker;
 };
 
+struct kthread_delayed_work {
+	struct kthread_work work;
+	struct timer_list timer;
+};
+
 #define INIT_KTHREAD_WORKER(worker)	{				\
 	.lock = __SPIN_LOCK_UNLOCKED((worker).lock),			\
 	.work_list = LIST_HEAD_INIT((worker).work_list),		\
+	.delayed_work_list = LIST_HEAD_INIT((worker).delayed_work_list),\
 	}
 
 #define INIT_KTHREAD_WORK(work, fn)	{				\

@@ -87,12 +95,23 @@ struct kthread_work {
 	.func = (fn),							\
 	}
 
+#define INIT_KTHREAD_DELAYED_WORK(dwork, fn) {				\
+	.work = INIT_KTHREAD_WORK((dwork).work, (fn)),			\
+	.timer = __TIMER_INITIALIZER(kthread_delayed_work_timer_fn,	\
+				     0, (unsigned long)&(dwork),	\
+				     TIMER_IRQSAFE),			\
+	}
+
 #define DEFINE_KTHREAD_WORKER(worker)					\
 	struct kthread_worker worker = INIT_KTHREAD_WORKER(worker)
 
 #define DEFINE_KTHREAD_WORK(work, fn)					\
 	struct kthread_work work = INIT_KTHREAD_WORK(work, fn)
 
+#define DEFINE_KTHREAD_DELAYED_WORK(dwork, fn)				\
+	struct kthread_delayed_work dwork =				\
+		INIT_KTHREAD_DELAYED_WORK(dwork, fn)
+
 /*
  * kthread_worker.lock needs its own lockdep class key when defined on
  * stack with lockdep enabled.  Use the following macros in such cases.

@@ -122,6 +141,15 @@ extern void __kthread_init_worker(struct kthread_worker *worker,
 		(work)->func = (fn);					\
 	} while (0)
 
+#define kthread_init_delayed_work(dwork, fn)				\
+	do {								\
+		kthread_init_work(&(dwork)->work, (fn));		\
+		__setup_timer(&(dwork)->timer,				\
+			      kthread_delayed_work_timer_fn,		\
+			      (unsigned long)(dwork),			\
+			      TIMER_IRQSAFE);				\
+	} while (0)
+
 int kthread_worker_fn(void *worker_ptr);
 
 __printf(1, 2)

@@ -133,6 +161,11 @@ kthread_create_worker_on_cpu(int cpu, const char namefmt[], ...);
 
 bool kthread_queue_work(struct kthread_worker *worker,
 			struct kthread_work *work);
+
+bool kthread_queue_delayed_work(struct kthread_worker *worker,
+				struct kthread_delayed_work *dwork,
+				unsigned long delay);
+
 void kthread_flush_work(struct kthread_work *work);
 void kthread_flush_worker(struct kthread_worker *worker);
 void kthread_drain_worker(struct kthread_worker *worker);

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 8e9548649c86..0336b378a5b9 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c

@@ -559,6 +559,7 @@ void __kthread_init_worker(struct kthread_worker *worker,
 	spin_lock_init(&worker->lock);
 	lockdep_set_class_and_name(&worker->lock, key, name);
 	INIT_LIST_HEAD(&worker->work_list);
+	INIT_LIST_HEAD(&worker->delayed_work_list);
 	worker->task = NULL;
 }
 EXPORT_SYMBOL_GPL(__kthread_init_worker);

@@ -763,6 +764,107 @@ bool kthread_queue_work(struct kthread_worker *worker,
 }
 EXPORT_SYMBOL_GPL(kthread_queue_work);
 
+/**
+ * kthread_delayed_work_timer_fn - callback that queues the associated kthread
+ *	delayed work when the timer expires.
+ * @__data: pointer to the data associated with the timer
+ *
+ * The format of the function is defined by struct timer_list.
+ * It should have been called from irqsafe timer with irq already off.
+ */
+void kthread_delayed_work_timer_fn(unsigned long __data)
+{
+	struct kthread_delayed_work *dwork =
+		(struct kthread_delayed_work *)__data;
+	struct kthread_work *work = &dwork->work;
+	struct kthread_worker *worker = work->worker;
+
+	/*
+	 * This might happen when a pending work is reinitialized.
+	 * It means that it is used a wrong way.
+	 */
+	if (WARN_ON_ONCE(!worker))
+		return;
+
+	spin_lock(&worker->lock);
+	/* Work must not be used with more workers, see kthread_queue_work(). */
+	WARN_ON_ONCE(work->worker != worker);
+
+	/* Move the work from worker->delayed_work_list. */
+	WARN_ON_ONCE(list_empty(&work->node));
+	list_del_init(&work->node);
+	kthread_insert_work(worker, work, &worker->work_list);
+
+	spin_unlock(&worker->lock);
+}
+EXPORT_SYMBOL(kthread_delayed_work_timer_fn);
+
+void __kthread_queue_delayed_work(struct kthread_worker *worker,
+				  struct kthread_delayed_work *dwork,
+				  unsigned long delay)
+{
+	struct timer_list *timer = &dwork->timer;
+	struct kthread_work *work = &dwork->work;
+
+	WARN_ON_ONCE(timer->function != kthread_delayed_work_timer_fn ||
+		     timer->data != (unsigned long)dwork);
+
+	/*
+	 * If @delay is 0, queue @dwork->work immediately.  This is for
+	 * both optimization and correctness.  The earliest @timer can
+	 * expire is on the closest next tick and delayed_work users depend
+	 * on that there's no such delay when @delay is 0.
+	 */
+	if (!delay) {
+		kthread_insert_work(worker, work, &worker->work_list);
+		return;
+	}
+
+	/* Be paranoid and try to detect possible races already now. */
+	kthread_insert_work_sanity_check(worker, work);
+
+	list_add(&work->node, &worker->delayed_work_list);
+	work->worker = worker;
+	timer_stats_timer_set_start_info(&dwork->timer);
+	timer->expires = jiffies + delay;
+	add_timer(timer);
+}
+
+/**
+ * kthread_queue_delayed_work - queue the associated kthread work
+ *	after a delay.
+ * @worker: target kthread_worker
+ * @dwork: kthread_delayed_work to queue
+ * @delay: number of jiffies to wait before queuing
+ *
+ * If the work has not been pending it starts a timer that will queue
+ * the work after the given @delay. If @delay is zero, it queues the
+ * work immediately.
+ *
+ * Return: %false if the @work has already been pending. It means that
+ * either the timer was running or the work was queued. It returns %true
+ * otherwise.
+ */
+bool kthread_queue_delayed_work(struct kthread_worker *worker,
+				struct kthread_delayed_work *dwork,
+				unsigned long delay)
+{
+	struct kthread_work *work = &dwork->work;
+	unsigned long flags;
+	bool ret = false;
+
+	spin_lock_irqsave(&worker->lock, flags);
+
+	if (list_empty(&work->node)) {
+		__kthread_queue_delayed_work(worker, dwork, delay);
+		ret = true;
+	}
+
+	spin_unlock_irqrestore(&worker->lock, flags);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(kthread_queue_delayed_work);
+
 struct kthread_flush_work {
 	struct kthread_work	work;
 	struct completion	done;

-- 
1.8.5.6

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[PATCH v9 11/12] kthread: Allow to modify delayed kthread work

From: Petr Mladek <pmladek@suse.com>
Date: 2016-06-16 11:19:48

There are situations when we need to modify the delay of a delayed kthread
work. For example, when the work depends on an event and the initial delay
means a timeout. Then we want to queue the work immediately when the event
happens.

This patch implements kthread_mod_delayed_work() as inspired workqueues.
It cancels the timer, removes the work from any worker list and queues it
again with the given timeout.

A very special case is when the work is being canceled at the same time.
It might happen because of the regular kthread_cancel_delayed_work_sync()
or by another kthread_mod_delayed_work(). In this case, we do nothing and
let the other operation win. This should not normally happen as the caller
is supposed to synchronize these operations a reasonable way.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 include/linux/kthread.h |  4 ++++
 kernel/kthread.c        | 53 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 89d4f188d9fe..4a606767ebf8 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h

@@ -168,6 +168,10 @@ bool kthread_queue_delayed_work(struct kthread_worker *worker,
 				struct kthread_delayed_work *dwork,
 				unsigned long delay);
 
+bool kthread_mod_delayed_work(struct kthread_worker *worker,
+			      struct kthread_delayed_work *dwork,
+			      unsigned long delay);
+
 void kthread_flush_work(struct kthread_work *work);
 void kthread_flush_worker(struct kthread_worker *worker);
 void kthread_drain_worker(struct kthread_worker *worker);

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 4c29340c8010..3b1d0bfe312d 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c

@@ -971,6 +971,59 @@ static bool __kthread_cancel_work(struct kthread_work *work, bool is_dwork,
 	return false;
 }
 
+/**
+ * kthread_mod_delayed_work - modify delay of or queue a kthread delayed work
+ * @worker: kthread worker to use
+ * @dwork: kthread delayed work to queue
+ * @delay: number of jiffies to wait before queuing
+ *
+ * If @dwork is idle, equivalent to kthread_queue_delayed_work(). Otherwise,
+ * modify @dwork's timer so that it expires after @delay. If @delay is zero,
+ * @work is guaranteed to be queued immediately.
+ *
+ * Return: %true if @dwork was pending and its timer was modified,
+ * %false otherwise.
+ *
+ * A special case is when the work is being canceled in parallel.
+ * It might be caused either by the real kthread_cancel_delayed_work_sync()
+ * or yet another kthread_mod_delayed_work() call. We let the other command
+ * win and return %false here. The caller is supposed to synchronize these
+ * operations a reasonable way.
+ *
+ * This function is safe to call from any context including IRQ handler.
+ * See __kthread_cancel_work() and kthread_delayed_work_timer_fn()
+ * for details.
+ */
+bool kthread_mod_delayed_work(struct kthread_worker *worker,
+			      struct kthread_delayed_work *dwork,
+			      unsigned long delay)
+{
+	struct kthread_work *work = &dwork->work;
+	unsigned long flags;
+	int ret = false;
+
+	spin_lock_irqsave(&worker->lock, flags);
+
+	/* Do not bother with canceling when never queued. */
+	if (!work->worker)
+		goto fast_queue;
+
+	/* Work must not be used with more workers, see kthread_queue_work() */
+	WARN_ON_ONCE(work->worker != worker);
+
+	/* Do not fight with another command that is canceling this work. */
+	if (work->canceling)
+		goto out;
+
+	ret = __kthread_cancel_work(work, true, &flags);
+fast_queue:
+	__kthread_queue_delayed_work(worker, dwork, delay);
+out:
+	spin_unlock_irqrestore(&worker->lock, flags);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(kthread_mod_delayed_work);
+
 static bool __kthread_cancel_work_sync(struct kthread_work *work, bool is_dwork)
 {
 	struct kthread_worker *worker = work->worker;

-- 
1.8.5.6

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[PATCH v9 12/12] kthread: Better support freezable kthread workers

From: Petr Mladek <pmladek@suse.com>
Date: 2016-06-16 11:19:50

This patch allows to make kthread worker freezable via a new @flags
parameter. It will allow to avoid an init work in some kthreads.

It currently does not affect the function of kthread_worker_fn()
but it might help to do some optimization or fixes eventually.

I currently do not know about any other use for the @flags
parameter but I believe that we will want more flags
in the future.

Finally, I hope that it will not cause confusion with @flags member
in struct kthread. Well, I guess that we will want to rework the
basic kthreads implementation once all kthreads are converted into
kthread workers or workqueues. It is possible that we will merge
the two structures.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 include/linux/kthread.h | 12 +++++++++---
 kernel/kthread.c        | 21 +++++++++++++++------
 2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 4a606767ebf8..60b45b0a291a 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h

@@ -65,7 +65,12 @@ struct kthread_work;
 typedef void (*kthread_work_func_t)(struct kthread_work *work);
 void kthread_delayed_work_timer_fn(unsigned long __data);
 
+enum {
+	KTW_FREEZABLE		= 1 << 0,	/* freeze during suspend */
+};
+
 struct kthread_worker {
+	unsigned int		flags;
 	spinlock_t		lock;
 	struct list_head	work_list;
 	struct list_head	delayed_work_list;

@@ -154,12 +159,13 @@ extern void __kthread_init_worker(struct kthread_worker *worker,
 
 int kthread_worker_fn(void *worker_ptr);
 
-__printf(1, 2)
+__printf(2, 3)
 struct kthread_worker *
-kthread_create_worker(const char namefmt[], ...);
+kthread_create_worker(unsigned int flags, const char namefmt[], ...);
 
 struct kthread_worker *
-kthread_create_worker_on_cpu(int cpu, const char namefmt[], ...);
+kthread_create_worker_on_cpu(int cpu, unsigned int flags,
+			     const char namefmt[], ...);
 
 bool kthread_queue_work(struct kthread_worker *worker,
 			struct kthread_work *work);

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 3b1d0bfe312d..881d748beccc 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c

@@ -556,11 +556,11 @@ void __kthread_init_worker(struct kthread_worker *worker,
 				const char *name,
 				struct lock_class_key *key)
 {
+	memset(worker, 0, sizeof(struct kthread_worker));
 	spin_lock_init(&worker->lock);
 	lockdep_set_class_and_name(&worker->lock, key, name);
 	INIT_LIST_HEAD(&worker->work_list);
 	INIT_LIST_HEAD(&worker->delayed_work_list);
-	worker->task = NULL;
 }
 EXPORT_SYMBOL_GPL(__kthread_init_worker);

@@ -590,6 +590,10 @@ int kthread_worker_fn(void *worker_ptr)
 	 */
 	WARN_ON(worker->task && worker->task != current);
 	worker->task = current;
+
+	if (worker->flags & KTW_FREEZABLE)
+		set_freezable();
+
 repeat:
 	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */

@@ -623,7 +627,8 @@ repeat:
 EXPORT_SYMBOL_GPL(kthread_worker_fn);
 
 static struct kthread_worker *
-__kthread_create_worker(int cpu, const char namefmt[], va_list args)
+__kthread_create_worker(int cpu, unsigned int flags,
+			const char namefmt[], va_list args)
 {
 	struct kthread_worker *worker;
 	struct task_struct *task;

@@ -653,6 +658,7 @@ __kthread_create_worker(int cpu, const char namefmt[], va_list args)
 	if (IS_ERR(task))
 		goto fail_task;
 
+	worker->flags = flags;
 	worker->task = task;
 	wake_up_process(task);
 	return worker;

@@ -664,6 +670,7 @@ fail_task:
 
 /**
  * kthread_create_worker - create a kthread worker
+ * @flags: flags modifying the default behavior of the worker
  * @namefmt: printf-style name for the kthread worker (task).
  *
  * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)

@@ -671,13 +678,13 @@ fail_task:
  * when the worker was SIGKILLed.
  */
 struct kthread_worker *
-kthread_create_worker(const char namefmt[], ...)
+kthread_create_worker(unsigned int flags, const char namefmt[], ...)
 {
 	struct kthread_worker *worker;
 	va_list args;
 
 	va_start(args, namefmt);
-	worker = __kthread_create_worker(-1, namefmt, args);
+	worker = __kthread_create_worker(-1, flags, namefmt, args);
 	va_end(args);
 
 	return worker;

@@ -688,6 +695,7 @@ EXPORT_SYMBOL(kthread_create_worker);
  * kthread_create_worker_on_cpu - create a kthread worker and bind it
  *	it to a given CPU and the associated NUMA node.
  * @cpu: CPU number
+ * @flags: flags modifying the default behavior of the worker
  * @namefmt: printf-style name for the kthread worker (task).
  *
  * Use a valid CPU number if you want to bind the kthread worker

@@ -701,13 +709,14 @@ EXPORT_SYMBOL(kthread_create_worker);
  * when the worker was SIGKILLed.
  */
 struct kthread_worker *
-kthread_create_worker_on_cpu(int cpu, const char namefmt[], ...)
+kthread_create_worker_on_cpu(int cpu, unsigned int flags,
+			     const char namefmt[], ...)
 {
 	struct kthread_worker *worker;
 	va_list args;
 
 	va_start(args, namefmt);
-	worker = __kthread_create_worker(cpu, namefmt, args);
+	worker = __kthread_create_worker(cpu, flags, namefmt, args);
 	va_end(args);
 
 	return worker;

-- 
1.8.5.6

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[PATCH v9 10/12] kthread: Allow to cancel kthread work

From: Petr Mladek <pmladek@suse.com>
Date: 2016-06-16 11:20:38

We are going to use kthread workers more widely and sometimes we will need
to make sure that the work is neither pending nor running.

This patch implements cancel_*_sync() operations as inspired by
workqueues. Well, we are synchronized against the other operations
via the worker lock, we use del_timer_sync() and a counter to count
parallel cancel operations. Therefore the implementation might be easier.

First, we check if a worker is assigned. If not, the work has newer
been queued after it was initialized.

Second, we take the worker lock. It must be the right one. The work must
not be assigned to another worker unless it is initialized in between.

Third, we try to cancel the timer when it exists. The timer is deleted
synchronously to make sure that the timer call back is not running.
We need to temporary release the worker->lock to avoid a possible
deadlock with the callback. In the meantime, we set work->canceling
counter to avoid any queuing.

Fourth, we try to remove the work from a worker list. It might be
the list of either normal or delayed works.

Fifth, if the work is running, we call kthread_flush_work(). It might
take an arbitrary time. We need to release the worker-lock again.
In the meantime, we again block any queuing by the canceling counter.

As already mentioned, the check for a pending kthread work is done under
a lock. In compare with workqueues, we do not need to fight for a single
PENDING bit to block other operations. Therefore we do not suffer from
the thundering storm problem and all parallel canceling jobs might use
kthread_flush_work(). Any queuing is blocked until the counter gets zero.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 include/linux/kthread.h |   5 ++
 kernel/kthread.c        | 131 +++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 134 insertions(+), 2 deletions(-)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 98d167187013..89d4f188d9fe 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h

@@ -77,6 +77,8 @@ struct kthread_work {
 	struct list_head	node;
 	kthread_work_func_t	func;
 	struct kthread_worker	*worker;
+	/* Number of canceling calls that are running at the moment. */
+	int			canceling;
 };
 
 struct kthread_delayed_work {

@@ -170,6 +172,9 @@ void kthread_flush_work(struct kthread_work *work);
 void kthread_flush_worker(struct kthread_worker *worker);
 void kthread_drain_worker(struct kthread_worker *worker);
 
+bool kthread_cancel_work_sync(struct kthread_work *work);
+bool kthread_cancel_delayed_work_sync(struct kthread_delayed_work *work);
+
 void kthread_destroy_worker(struct kthread_worker *worker);
 
 #endif /* _LINUX_KTHREAD_H */

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 0336b378a5b9..4c29340c8010 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c

@@ -714,6 +714,18 @@ kthread_create_worker_on_cpu(int cpu, const char namefmt[], ...)
 }
 EXPORT_SYMBOL(kthread_create_worker_on_cpu);
 
+/*
+ * Returns true when the work could not be queued at the moment.
+ * It happens when it is already pending in a worker list
+ * or when it is being cancelled.
+ *
+ * This function must be called under work->worker->lock.
+ */
+static inline bool queuing_blocked(const struct kthread_work *work)
+{
+	return !list_empty(&work->node) || work->canceling;
+}
+
 static void kthread_insert_work_sanity_check(struct kthread_worker *worker,
 					     struct kthread_work *work)
 {

@@ -755,7 +767,7 @@ bool kthread_queue_work(struct kthread_worker *worker,
 	unsigned long flags;
 
 	spin_lock_irqsave(&worker->lock, flags);
-	if (list_empty(&work->node)) {
+	if (!queuing_blocked(work)) {
 		kthread_insert_work(worker, work, &worker->work_list);
 		ret = true;
 	}

@@ -855,7 +867,7 @@ bool kthread_queue_delayed_work(struct kthread_worker *worker,
 
 	spin_lock_irqsave(&worker->lock, flags);
 
-	if (list_empty(&work->node)) {
+	if (!queuing_blocked(work)) {
 		__kthread_queue_delayed_work(worker, dwork, delay);
 		ret = true;
 	}

@@ -915,6 +927,121 @@ void kthread_flush_work(struct kthread_work *work)
 }
 EXPORT_SYMBOL_GPL(kthread_flush_work);
 
+/*
+ * This function removes the work from the worker queue. Also it makes sure
+ * that it won't get queued later via the delayed work's timer.
+ *
+ * The work might still be in use when this function finishes. See the
+ * current_work proceed by the worker.
+ *
+ * Return: %true if @work was pending and successfully canceled,
+ *	%false if @work was not pending
+ */
+static bool __kthread_cancel_work(struct kthread_work *work, bool is_dwork,
+				  unsigned long *flags)
+{
+	/* Try to cancel the timer if exists. */
+	if (is_dwork) {
+		struct kthread_delayed_work *dwork =
+			container_of(work, struct kthread_delayed_work, work);
+		struct kthread_worker *worker = work->worker;
+
+		/*
+		 * del_timer_sync() must be called to make sure that the timer
+		 * callback is not running. The lock must be temporary released
+		 * to avoid a deadlock with the callback. In the meantime,
+		 * any queuing is blocked by setting the canceling counter.
+		 */
+		work->canceling++;
+		spin_unlock_irqrestore(&worker->lock, *flags);
+		del_timer_sync(&dwork->timer);
+		spin_lock_irqsave(&worker->lock, *flags);
+		work->canceling--;
+	}
+
+	/*
+	 * Try to remove the work from a worker list. It might either
+	 * be from worker->work_list or from worker->delayed_work_list.
+	 */
+	if (!list_empty(&work->node)) {
+		list_del_init(&work->node);
+		return true;
+	}
+
+	return false;
+}
+
+static bool __kthread_cancel_work_sync(struct kthread_work *work, bool is_dwork)
+{
+	struct kthread_worker *worker = work->worker;
+	unsigned long flags;
+	int ret = false;
+
+	if (!worker)
+		goto out;
+
+	spin_lock_irqsave(&worker->lock, flags);
+	/* Work must not be used with more workers, see kthread_queue_work(). */
+	WARN_ON_ONCE(work->worker != worker);
+
+	ret = __kthread_cancel_work(work, is_dwork, &flags);
+
+	if (worker->current_work != work)
+		goto out_fast;
+
+	/*
+	 * The work is in progress and we need to wait with the lock released.
+	 * In the meantime, block any queuing by setting the canceling counter.
+	 */
+	work->canceling++;
+	spin_unlock_irqrestore(&worker->lock, flags);
+	kthread_flush_work(work);
+	spin_lock_irqsave(&worker->lock, flags);
+	work->canceling--;
+
+out_fast:
+	spin_unlock_irqrestore(&worker->lock, flags);
+out:
+	return ret;
+}
+
+/**
+ * kthread_cancel_work_sync - cancel a kthread work and wait for it to finish
+ * @work: the kthread work to cancel
+ *
+ * Cancel @work and wait for its execution to finish.  This function
+ * can be used even if the work re-queues itself. On return from this
+ * function, @work is guaranteed to be not pending or executing on any CPU.
+ *
+ * kthread_cancel_work_sync(&delayed_work->work) must not be used for
+ * delayed_work's. Use kthread_cancel_delayed_work_sync() instead.
+ *
+ * The caller must ensure that the worker on which @work was last
+ * queued can't be destroyed before this function returns.
+ *
+ * Return: %true if @work was pending, %false otherwise.
+ */
+bool kthread_cancel_work_sync(struct kthread_work *work)
+{
+	return __kthread_cancel_work_sync(work, false);
+}
+EXPORT_SYMBOL_GPL(kthread_cancel_work_sync);
+
+/**
+ * kthread_cancel_delayed_work_sync - cancel a kthread delayed work and
+ *	wait for it to finish.
+ * @dwork: the kthread delayed work to cancel
+ *
+ * This is kthread_cancel_work_sync() for delayed works.
+ *
+ * Return: %true if @dwork was pending, %false otherwise.
+ */
+bool kthread_cancel_delayed_work_sync(struct kthread_delayed_work *dwork)
+{
+	return __kthread_cancel_work_sync(&dwork->work, true);
+}
+EXPORT_SYMBOL_GPL(kthread_cancel_delayed_work_sync);
+
 /**
  * kthread_flush_worker - flush all current works on a kthread_worker
  * @worker: worker to flush

-- 
1.8.5.6

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Re: [PATCH v9 02/12] kthread: Kthread worker API cleanup

From: Tejun Heo <tj@kernel.org>
Date: 2016-06-20 19:28:42

Hello,

On Thu, Jun 16, 2016 at 01:17:21PM +0200, Petr Mladek wrote:

__init_kthread_worker()		-> __kthread_init_worker()
init_kthread_worker()		-> kthread_init_worker()
init_kthread_work()		-> kthread_init_work()
insert_kthread_work()		-> kthread_insert_work()
queue_kthread_work()		-> kthread_queue_work()
flush_kthread_work()		-> kthread_flush_work()
flush_kthread_worker()		-> kthread_flush_worker()

I wonder whether the subsystem name here is more the whole
kthread_worker rather than just kthread but I can't think of a good
single syllable abbrev for it.  It's a bikeshedding anyway.

Note that the names of DEFINE_KTHREAD_WORK*() macros stay
as they are. It is common that the "DEFINE_" prefix has
precedence over the subsystem names.

INIT_() macros are similar to DEFINE_. Therefore this patch
renames:

KTHREAD_WORKER_INIT()		-> INIT_KTHREAD_WORKER()
KTHREAD_WORK_INIT()		-> INIT_KTHREAD_WORK()

So, they're different.  In the above cases, INIT doesn't stand for the
verb INITIALIZE but its noun form INITIALIZER.  These aren't
operations and thus different from DEFINE_XXX().

	kthread_init_worker	= kthread: initialize worker
	KTHREAD_WORKER_INIT	= kthread: worker initializer

I think it makes a lot more sense to keep _INIT at the end for these.

Thanks.

-- 
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Re: [PATCH v9 01/12] kthread: Rename probe_kthread_data() to kthread_probe_data()

From: Tejun Heo <tj@kernel.org>
Date: 2016-06-20 19:29:11

On Thu, Jun 16, 2016 at 01:17:20PM +0200, Petr Mladek wrote:

A good practice is to prefix the names of functions by the name
of the subsystem.

This patch fixes the name of probe_kthread_data(). The other wrong
functions names are part of the kthread worker API and will be
fixed separately.

Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

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Re: [PATCH v9 04/12] kthread: Allow to call __kthread_create_on_node() with va_list args

From: Tejun Heo <tj@kernel.org>
Date: 2016-06-20 19:51:51

On Thu, Jun 16, 2016 at 01:17:23PM +0200, Petr Mladek wrote:

kthread_create_on_node() implements a bunch of logic to create
the kthread. It is already called by kthread_create_on_cpu().

We are going to extend the kthread worker API and will
need to call kthread_create_on_node() with va_list args there.

This patch does only a refactoring and does not modify the existing
behavior.

Signed-off-by: Petr Mladek <pmladek@suse.com>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

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Re: [PATCH v9 05/12] kthread: Add kthread_create_worker*()

From: Tejun Heo <tj@kernel.org>
Date: 2016-06-20 19:55:54

On Thu, Jun 16, 2016 at 01:17:24PM +0200, Petr Mladek wrote:

Kthread workers are currently created using the classic kthread API,
namely kthread_run(). kthread_worker_fn() is passed as the @threadfn
parameter.

This patch defines kthread_create_worker() and
kthread_create_worker_on_cpu() functions that hide implementation details.

They enforce using kthread_worker_fn() for the main thread. But I doubt
that there are any plans to create any alternative. In fact, I think
that we do not want any alternative main thread because it would be
hard to support consistency with the rest of the kthread worker API.

The naming and function of kthread_create_worker() is inspired by
the workqueues API like the rest of the kthread worker API.

The kthread_create_worker_on_cpu() variant is motivated by the original
kthread_create_on_cpu(). Note that we need to bind per-CPU kthread
workers already when they are created. It makes the life easier.
kthread_bind() could not be used later for an already running worker.

This patch does _not_ convert existing kthread workers. The kthread worker
API need more improvements first, e.g. a function to destroy the worker.

IMPORTANT:

kthread_create_worker_on_cpu() allows to use any format of the
worker name, in compare with kthread_create_on_cpu(). The good thing
is that it is more generic. The bad thing is that most users will
need to pass the cpu number in two parameters, e.g.
kthread_create_worker_on_cpu(cpu, "helper/%d", cpu).

To be honest, the main motivation was to avoid the need for an
empty va_list. The only legal way was to create a helper function that
would be called with an empty list. Other attempts caused compilation
warnings or even errors on different architectures.

There were also other alternatives, for example, using #define or
splitting __kthread_create_worker(). The used solution looked
like the least ugly.

Signed-off-by: Petr Mladek <pmladek@suse.com>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

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Re: [PATCH v9 06/12] kthread: Add kthread_drain_worker()

From: Tejun Heo <tj@kernel.org>
Date: 2016-06-20 19:57:25

On Thu, Jun 16, 2016 at 01:17:25PM +0200, Petr Mladek wrote:

kthread_flush_worker() returns when the currently queued works are proceed.
But some other works might have been queued in the meantime.

This patch adds kthread_drain_worker() that is inspired by
drain_workqueue(). It returns when the queue is completely
empty and warns when it takes too long.

The initial implementation does not block queuing new works when
draining. It makes things much easier. The blocking would be useful
to debug potential problems but it is not clear if it is worth
the complication at the moment.

Signed-off-by: Petr Mladek <pmladek@suse.com>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
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Re: [PATCH v9 07/12] kthread: Add kthread_destroy_worker()

From: Tejun Heo <tj@kernel.org>
Date: 2016-06-20 19:58:17

On Thu, Jun 16, 2016 at 01:17:26PM +0200, Petr Mladek wrote:

The current kthread worker users call flush() and stop() explicitly.
This function drains the worker, stops it, and frees the kthread_worker
struct in one call.

It is supposed to be used together with kthread_create_worker*() that
allocates struct kthread_worker.

Also note that drain() correctly handles self-queuing works in compare
with flush().

Signed-off-by: Petr Mladek <pmladek@suse.com>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

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Re: [PATCH v9 08/12] kthread: Detect when a kthread work is used by more workers

From: Tejun Heo <tj@kernel.org>
Date: 2016-06-20 20:12:55

Hello,

On Thu, Jun 16, 2016 at 01:17:27PM +0200, Petr Mladek wrote:

quoted hunk

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 567ec49b4872..8e9548649c86 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c

@@ -574,6 +574,9 @@ EXPORT_SYMBOL_GPL(__kthread_init_worker);
  * The works are not allowed to keep any locks, disable preemption or interrupts
  * when they finish. There is defined a safe point for freezing when one work
  * finishes and before a new one is started.
+ *
+ * Also the works must not be handled by more workers at the same time, see also

                                                ^
						than one

quoted hunk

+ * kthread_queue_work().
  */
 int kthread_worker_fn(void *worker_ptr)
 {

@@ -710,12 +713,21 @@ kthread_create_worker_on_cpu(int cpu, const char namefmt[], ...)
 }
 EXPORT_SYMBOL(kthread_create_worker_on_cpu);
 
+static void kthread_insert_work_sanity_check(struct kthread_worker *worker,
+					     struct kthread_work *work)
+{
+	lockdep_assert_held(&worker->lock);
+	WARN_ON_ONCE(!list_empty(&work->node));
+	/* Do not use a work with more workers, see kthread_queue_work() */

                                  ^
				  ditto, maybe just say ">1 workers"?

Looks good otherwise.

Thanks.

-- 
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Re: [PATCH v9 09/12] kthread: Initial support for delayed kthread work

From: Tejun Heo <tj@kernel.org>
Date: 2016-06-20 20:23:10

Hello,

On Thu, Jun 16, 2016 at 01:17:28PM +0200, Petr Mladek wrote:

+/**
+ * kthread_delayed_work_timer_fn - callback that queues the associated kthread
+ *	delayed work when the timer expires.
+ * @__data: pointer to the data associated with the timer
+ *
+ * The format of the function is defined by struct timer_list.
+ * It should have been called from irqsafe timer with irq already off.
+ */
+void kthread_delayed_work_timer_fn(unsigned long __data)
+{
+	struct kthread_delayed_work *dwork =
+		(struct kthread_delayed_work *)__data;
+	struct kthread_work *work = &dwork->work;
+	struct kthread_worker *worker = work->worker;
+
+	/*
+	 * This might happen when a pending work is reinitialized.
+	 * It means that it is used a wrong way.
+	 */
+	if (WARN_ON_ONCE(!worker))
+		return;
+
+	spin_lock(&worker->lock);
+	/* Work must not be used with more workers, see kthread_queue_work(). */

                                         ^
					 ditto, this reads weird

Other than that,

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

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Re: [PATCH v9 11/12] kthread: Allow to modify delayed kthread work

From: Tejun Heo <tj@kernel.org>
Date: 2016-06-20 20:29:42

On Thu, Jun 16, 2016 at 01:17:30PM +0200, Petr Mladek wrote:

There are situations when we need to modify the delay of a delayed kthread
work. For example, when the work depends on an event and the initial delay
means a timeout. Then we want to queue the work immediately when the event
happens.

This patch implements kthread_mod_delayed_work() as inspired workqueues.
It cancels the timer, removes the work from any worker list and queues it
again with the given timeout.

A very special case is when the work is being canceled at the same time.
It might happen because of the regular kthread_cancel_delayed_work_sync()
or by another kthread_mod_delayed_work(). In this case, we do nothing and
let the other operation win. This should not normally happen as the caller
is supposed to synchronize these operations a reasonable way.

Signed-off-by: Petr Mladek <pmladek@suse.com>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

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Re: [PATCH v9 12/12] kthread: Better support freezable kthread workers

From: Tejun Heo <tj@kernel.org>
Date: 2016-06-20 20:30:12

On Thu, Jun 16, 2016 at 01:17:31PM +0200, Petr Mladek wrote:

This patch allows to make kthread worker freezable via a new @flags
parameter. It will allow to avoid an init work in some kthreads.

It currently does not affect the function of kthread_worker_fn()
but it might help to do some optimization or fixes eventually.

I currently do not know about any other use for the @flags
parameter but I believe that we will want more flags
in the future.

Finally, I hope that it will not cause confusion with @flags member
in struct kthread. Well, I guess that we will want to rework the
basic kthreads implementation once all kthreads are converted into
kthread workers or workqueues. It is possible that we will merge
the two structures.

Signed-off-by: Petr Mladek <pmladek@suse.com>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

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Re: [PATCH v9 10/12] kthread: Allow to cancel kthread work

From: Tejun Heo <tj@kernel.org>
Date: 2016-06-20 20:46:17

On Thu, Jun 16, 2016 at 01:17:29PM +0200, Petr Mladek wrote:

+/*
+ * Returns true when the work could not be queued at the moment.
+ * It happens when it is already pending in a worker list
+ * or when it is being cancelled.
+ *
+ * This function must be called under work->worker->lock.

Replace the comment with a lockdep assertion?

+ */
+static inline bool queuing_blocked(const struct kthread_work *work)
+{
+	return !list_empty(&work->node) || work->canceling;
+}

Other than that,

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

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Re: [PATCH v9 06/12] kthread: Add kthread_drain_worker()

From: Peter Zijlstra <peterz@infradead.org>
Date: 2016-06-22 20:54:54

On Thu, Jun 16, 2016 at 01:17:25PM +0200, Petr Mladek wrote:

+/**
+ * kthread_drain_worker - drain a kthread worker
+ * @worker: worker to be drained
+ *
+ * Wait until there is no work queued for the given kthread worker.
+ * @worker is flushed repeatedly until it becomes empty.  The number
+ * of flushing is determined by the depth of chaining and should
+ * be relatively short.  Whine if it takes too long.
+ *

+ * The caller is responsible for blocking all users of this kthread
+ * worker from queuing new works. Also it is responsible for blocking
+ * the already queued works from an infinite re-queuing!

This, I really dislike that. And it makes the kthread_destroy_worker()
from the next patch unnecessarily fragile.

Why not add a kthread_worker::blocked flag somewhere and refuse/WARN
kthread_queue_work() when that is set.

+ */
+void kthread_drain_worker(struct kthread_worker *worker)
+{
+	int flush_cnt = 0;
+
+	spin_lock_irq(&worker->lock);
+
+	while (!list_empty(&worker->work_list)) {
+		spin_unlock_irq(&worker->lock);
+
+		kthread_flush_worker(worker);
+		WARN_ONCE(flush_cnt++ > 10,
+			  "kthread worker %s: kthread_drain_worker() isn't complete after %u tries\n",
+			  worker->task->comm, flush_cnt);
+
+		spin_lock_irq(&worker->lock);
+	}
+
+	spin_unlock_irq(&worker->lock);
+}
+EXPORT_SYMBOL(kthread_drain_worker);
-- 
1.8.5.6

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Re: [PATCH v9 06/12] kthread: Add kthread_drain_worker()

From: Tejun Heo <tj@kernel.org>
Date: 2016-06-23 21:33:03

Hello,

On Wed, Jun 22, 2016 at 10:54:45PM +0200, Peter Zijlstra wrote:

quoted

+ * The caller is responsible for blocking all users of this kthread
+ * worker from queuing new works. Also it is responsible for blocking
+ * the already queued works from an infinite re-queuing!

This, I really dislike that. And it makes the kthread_destroy_worker()
from the next patch unnecessarily fragile.

Why not add a kthread_worker::blocked flag somewhere and refuse/WARN
kthread_queue_work() when that is set.

It's the same logic from workqueue counterpart.  For workqueue,
nothing can make it less fragile as the workqueue struct itself is
freed on destruction.  If its users fail to stop issuing work items,
it'll lead to use-after-free.

IIRC, the draining of self-requeueing work items is a specific
requirement from some edge use case which used workqueue to implement
multi-step state machine.  Given how rare that is and the extra
complexity of identifying self-requeueing cases, let's forget about
draining and on destruction clear the worker pointer to block further
queueing and then flush whatever is in flight.

Thanks.

-- 
tejun

Re: [PATCH v9 06/12] kthread: Add kthread_drain_worker()

From: Peter Zijlstra <peterz@infradead.org>
Date: 2016-06-24 07:05:30

On Thu, Jun 23, 2016 at 05:32:58PM -0400, Tejun Heo wrote:

Hello,

On Wed, Jun 22, 2016 at 10:54:45PM +0200, Peter Zijlstra wrote:

quoted

+ * The caller is responsible for blocking all users of this kthread
+ * worker from queuing new works. Also it is responsible for blocking
+ * the already queued works from an infinite re-queuing!

This, I really dislike that. And it makes the kthread_destroy_worker()
from the next patch unnecessarily fragile.

Why not add a kthread_worker::blocked flag somewhere and refuse/WARN
kthread_queue_work() when that is set.

It's the same logic from workqueue counterpart.

So ? Clearly it (the kthread workqueue) can be improved here.

For workqueue, nothing can make it less fragile as the workqueue
struct itself is freed on destruction.  If its users fail to stop
issuing work items, it'll lead to use-after-free.

Right, but this kthread thingy does not, so why not add a failsafe?

IIRC, the draining of self-requeueing work items is a specific
requirement from some edge use case which used workqueue to implement
multi-step state machine.

Right, that might be an issue,

Given how rare that is

Could you then not remove/rework these few cases for workqueue as well
and make that 'better' too?

and the extra
complexity of identifying self-requeueing cases, let's forget about
draining and on destruction clear the worker pointer to block further
queueing and then flush whatever is in flight.

You're talking about regular workqueues here?

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Re: [PATCH v9 06/12] kthread: Add kthread_drain_worker()

From: Petr Mladek <pmladek@suse.com>
Date: 2016-06-24 09:08:32

On Fri 2016-06-24 09:05:15, Peter Zijlstra wrote:

On Thu, Jun 23, 2016 at 05:32:58PM -0400, Tejun Heo wrote:

quoted

Hello,

On Wed, Jun 22, 2016 at 10:54:45PM +0200, Peter Zijlstra wrote:

quoted

+ * The caller is responsible for blocking all users of this kthread
+ * worker from queuing new works. Also it is responsible for blocking
+ * the already queued works from an infinite re-queuing!

This, I really dislike that. And it makes the kthread_destroy_worker()
from the next patch unnecessarily fragile.

Why not add a kthread_worker::blocked flag somewhere and refuse/WARN
kthread_queue_work() when that is set.

It's the same logic from workqueue counterpart.

So ? Clearly it (the kthread workqueue) can be improved here.

quoted

For workqueue, nothing can make it less fragile as the workqueue
struct itself is freed on destruction.  If its users fail to stop
issuing work items, it'll lead to use-after-free.

Right, but this kthread thingy does not, so why not add a failsafe?

The struct kthread_worker is freed in kthread_destroy_worker().
So kthread_worker is the same situation as workqueues.

The allocation/freeing has been added in v2. It helped
to make it clear when the structure was initialized. Note that we
still need the crate/destroy functions to start/stop the kthread.
See the discussion at
https://lkml.kernel.org/g/20150728172657.GC5322@mtj.duckdns.org

I personally do not have strong opinion about it.

On one hand, it makes the code more complex because we need strong
synchronization between queueing/canceling/destroying. There are cases
where it is not that important, for example the hugepage daemon or
hung task. It does not matter if the next round will be done or not.
Well, it is strange if someting gets queued and it is not proceed.

On the other hand, there are situations where the work must be
done, e.g. some I/O operation. They need the strong syncronization.
We could print a warning when queueing a work for a destroyed
(stoped) kthread_worker to catch potential problems. But then we will need
the strong synchronization in all cases to avoid "false" alarms.

After all, the blocked flag will not necessarily make the usage
less hairy. Or did I miss something?

Best Regards,
Petr

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Re: [PATCH v9 06/12] kthread: Add kthread_drain_worker()

From: Tejun Heo <tj@kernel.org>
Date: 2016-06-24 15:54:52

Hello,

On Fri, Jun 24, 2016 at 09:05:15AM +0200, Peter Zijlstra wrote:

quoted

Given how rare that is

Could you then not remove/rework these few cases for workqueue as well
and make that 'better' too?

Usage of draining is rare for workqueue but that still means several
legitimate users.  With draining there, it's logical to use it during
shutdown.  I don't think it makes sense to change it on workqueue
side.

quoted

and the extra
complexity of identifying self-requeueing cases, let's forget about
draining and on destruction clear the worker pointer to block further
queueing and then flush whatever is in flight.

You're talking about regular workqueues here?

No, kthread worker.  It's unlikely that kthread worker is gonna need
chained draining especially given that most of its usages are gonna be
conversions from raw kthread usages.  We won't lose much if anything
by just ignoring draining and making the code simpler.

Thanks.

-- 
tejun

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Re: [PATCH v9 06/12] kthread: Add kthread_drain_worker()

From: Petr Mladek <pmladek@suse.com>
Date: 2016-06-27 14:33:55

Hi,

On Fri 2016-06-24 11:54:47, Tejun Heo wrote:

On Fri, Jun 24, 2016 at 09:05:15AM +0200, Peter Zijlstra wrote:

quoted

Given how rare that is

Could you then not remove/rework these few cases for workqueue as well
and make that 'better' too?

Usage of draining is rare for workqueue but that still means several
legitimate users.  With draining there, it's logical to use it during
shutdown.  I don't think it makes sense to change it on workqueue
side.

quoted

and the extra
complexity of identifying self-requeueing cases, let's forget about
draining and on destruction clear the worker pointer to block further
queueing and then flush whatever is in flight.

You're talking about regular workqueues here?

No, kthread worker.  It's unlikely that kthread worker is gonna need
chained draining especially given that most of its usages are gonna be
conversions from raw kthread usages.  We won't lose much if anything
by just ignoring draining and making the code simpler.

OK, so you suggest to do the following:

  1. Add a flag into struct kthread_worker that will prevent
     from further queuing.

  2. kthread_create_worker()/kthread_destroy_worker() will
     not longer dynamically allocate struct kthread_worker.
     They will just start/stop the kthread.


The result will be:

  a. User will not need the strict synchronization between
     the queue and create/destroy operations.

  b. We could get rid of drain_kthread_worker() because
     flush_kthread_worker() will be enough.


IMHO, the 1st change does not make sense without the 2nd one.
Otherwise, users could do an out-of-memory access when testing
the freed kthread_worker flag.

Do I get this correctly please?

Best Regards,
Petr

Re: [PATCH v9 06/12] kthread: Add kthread_drain_worker()

From: Tejun Heo <tj@kernel.org>
Date: 2016-06-28 17:05:39

Hello,

On Mon, Jun 27, 2016 at 04:33:50PM +0200, Petr Mladek wrote:

OK, so you suggest to do the following:

  1. Add a flag into struct kthread_worker that will prevent
     from further queuing.

This doesn't add any protection, right?  It's getting freed anyway.

  2. kthread_create_worker()/kthread_destroy_worker() will
     not longer dynamically allocate struct kthread_worker.
     They will just start/stop the kthread.

Ah, okay, I don't think we need to change this.  I was suggesting to
simplify it by dropping the draining and just do flush from destroy.

Thanks.

-- 
tejun

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Re: [PATCH v9 06/12] kthread: Add kthread_drain_worker()

From: Petr Mladek <pmladek@suse.com>
Date: 2016-06-29 08:18:12

On Tue 2016-06-28 13:04:47, Tejun Heo wrote:

Hello,

On Mon, Jun 27, 2016 at 04:33:50PM +0200, Petr Mladek wrote:

quoted

OK, so you suggest to do the following:

  1. Add a flag into struct kthread_worker that will prevent
     from further queuing.

This doesn't add any protection, right?  It's getting freed anyway.

quoted

  2. kthread_create_worker()/kthread_destroy_worker() will
     not longer dynamically allocate struct kthread_worker.
     They will just start/stop the kthread.

Ah, okay, I don't think we need to change this.  I was suggesting to
simplify it by dropping the draining and just do flush from destroy.

I see. But then it does not address the original concern from Peter
Zijlstra. He did not like that the caller was responsible for blocking
further queueing. It still will be needed. Or did I miss something,
please?

Best Regards,
Petr

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Re: [PATCH v9 06/12] kthread: Add kthread_drain_worker()

From: Tejun Heo <tj@kernel.org>
Date: 2016-06-29 13:16:06

Hello,

On Wed, Jun 29, 2016 at 10:17:48AM +0200, Petr Mladek wrote:

quoted

Ah, okay, I don't think we need to change this.  I was suggesting to
simplify it by dropping the draining and just do flush from destroy.

I see. But then it does not address the original concern from Peter
Zijlstra. He did not like that the caller was responsible for blocking
further queueing. It still will be needed. Or did I miss something,
please?

You can only protect against so much.  Let's say we make the worker
struct to be allocated by the user, what then prevents it prematurely
from user side?  Use-after-free is use-after-free.  If we can trivally
add some protection against it, great, but no need to contort the
design to add marginal protection.

Thanks.

-- 
tejun

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