blk-mq: fix hang caused by freeze/unfreeze sequence

Long time ago there was a similar fix proposed by Akinobu Mita[1],
but it seems that time everyone decided to fix this subtle race in
percpu-refcount and Tejun Heo[2] did an attempt (as I can see that
patchset was not applied).

The following is a description of a queue hang - same fix but a bug
from another angle.

The hang happens on queue freeze because of a simultaneous calls of
blk_mq_freeze_queue() and blk_mq_unfreeze_queue() from different threads,
and because of a reference race percpu_ref_reinit() and percpu_ref_kill()
swap.

 CPU#0             CPU#1
 ----------------  -----------------
 percpu_ref_kill()
 
                   percpu_ref_kill() << atomic reference does not
 percpu_ref_reinit()                 << guarantee the order

                   blk_mq_freeze_queue_wait() << HANG HERE

                   percpu_ref_reinit()

Firstly this wrong sequence raises two kernel warnings:

  1st. WARNING at lib/percpu-recount.c:309
       percpu_ref_kill_and_confirm called more than once

  2nd. WARNING at lib/percpu-refcount.c:331

But the most unpleasant effect is a hang of a blk_mq_freeze_queue_wait(),
which waits for a zero of a q_usage_counter, which never happens
because percpu-ref was not reinited and stays in PERCPU state forever.

The simplified sequence above is reproduced on shared tags, when one
queue is going to die meanwhile another one is initing:

 CPU#0                           CPU#1
 ------------------------------- ------------------------------------

25 more lines

diff --git a/block/blk-core.c b/block/blk-core.c
index ef78848..01dcb02 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c

@@ -740,6 +740,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
 	__set_bit(QUEUE_FLAG_BYPASS, &q->queue_flags);
 
 	init_waitqueue_head(&q->mq_freeze_wq);
+	mutex_init(&q->mq_freeze_lock);
 
 	/*
 	 * Init percpu_ref in atomic mode so that it's faster to shutdown.

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 6d6f8fe..1f3e81b 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c

@@ -80,13 +80,13 @@ static void blk_mq_hctx_clear_pending(struct blk_mq_hw_ctx *hctx,
 
 void blk_mq_freeze_queue_start(struct request_queue *q)
 {
-	int freeze_depth;
-
-	freeze_depth = atomic_inc_return(&q->mq_freeze_depth);
-	if (freeze_depth == 1) {
+	mutex_lock(&q->mq_freeze_lock);
+	if (++q->mq_freeze_depth == 1) {
 		percpu_ref_kill(&q->q_usage_counter);
+		mutex_unlock(&q->mq_freeze_lock);
 		blk_mq_run_hw_queues(q, false);
-	}
+	} else
+		mutex_unlock(&q->mq_freeze_lock);
 }
 EXPORT_SYMBOL_GPL(blk_mq_freeze_queue_start);
 

@@ -124,14 +124,14 @@ EXPORT_SYMBOL_GPL(blk_mq_freeze_queue);
 
 void blk_mq_unfreeze_queue(struct request_queue *q)
 {
-	int freeze_depth;
-
-	freeze_depth = atomic_dec_return(&q->mq_freeze_depth);
-	WARN_ON_ONCE(freeze_depth < 0);
-	if (!freeze_depth) {
+	mutex_lock(&q->mq_freeze_lock);
+	q->mq_freeze_depth--;
+	WARN_ON_ONCE(q->mq_freeze_depth < 0);
+	if (!q->mq_freeze_depth) {
 		percpu_ref_reinit(&q->q_usage_counter);
 		wake_up_all(&q->mq_freeze_wq);
 	}
+	mutex_unlock(&q->mq_freeze_lock);
 }
 EXPORT_SYMBOL_GPL(blk_mq_unfreeze_queue);
 

@@ -2105,7 +2105,7 @@ void blk_mq_free_queue(struct request_queue *q)
 static void blk_mq_queue_reinit(struct request_queue *q,
 				const struct cpumask *online_mask)
 {
-	WARN_ON_ONCE(!atomic_read(&q->mq_freeze_depth));
+	WARN_ON_ONCE(!q->mq_freeze_depth);
 
 	blk_mq_sysfs_unregister(q);
 

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index f6ff9d1..d692c16 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h

@@ -445,7 +445,7 @@ struct request_queue {
 	struct mutex		sysfs_lock;
 
 	int			bypass_depth;
-	atomic_t		mq_freeze_depth;
+	int			mq_freeze_depth;
 
 #if defined(CONFIG_BLK_DEV_BSG)
 	bsg_job_fn		*bsg_job_fn;

@@ -459,6 +459,11 @@ struct request_queue {
 #endif
 	struct rcu_head		rcu_head;
 	wait_queue_head_t	mq_freeze_wq;
+	/*
+	 * Protect concurrent access to q_usage_counter by
+	 * percpu_ref_kill() and percpu_ref_reinit().
+	 */
+	struct mutex		mq_freeze_lock;
 	struct percpu_ref	q_usage_counter;
 	struct list_head	all_q_node;
 

-- 
2.9.0

Hi Roman,

[auto build test ERROR on block/for-next]
[also build test ERROR on v4.7 next-20160805]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Roman-Pen/blk-mq-fix-hang-caused-by-freeze-unfreeze-sequence/20160806-014441
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
config: x86_64-randconfig-x015-201631 (attached as .config)
compiler: gcc-6 (Debian 6.1.1-9) 6.1.1 20160705
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All error/warnings (new ones prefixed by >>):

   In file included from include/linux/mmzone.h:9:0,
                    from include/linux/gfp.h:5,
                    from include/linux/kmod.h:22,
                    from include/linux/module.h:13,
                    from block/blk-core.c:15:
   block/blk-core.c: In function 'blk_queue_enter':

quoted

block/blk-core.c:661:18: error: passing argument 1 of 'atomic_read' from incompatible pointer type [-Werror=incompatible-pointer-types]

        !atomic_read(&q->mq_freeze_depth) ||
                     ^
   include/linux/wait.h:473:8: note: in definition of macro 'wait_event_interruptible'
     if (!(condition))      \
           ^~~~~~~~~
   In file included from arch/x86/include/asm/msr.h:66:0,
                    from arch/x86/include/asm/processor.h:20,
                    from arch/x86/include/asm/cpufeature.h:4,
                    from arch/x86/include/asm/thread_info.h:52,
                    from include/linux/thread_info.h:54,
                    from arch/x86/include/asm/preempt.h:6,
                    from include/linux/preempt.h:59,
                    from include/linux/spinlock.h:50,
                    from include/linux/seqlock.h:35,
                    from include/linux/time.h:5,
                    from include/linux/stat.h:18,
                    from include/linux/module.h:10,
                    from block/blk-core.c:15:
   arch/x86/include/asm/atomic.h:24:28: note: expected 'const atomic_t * {aka const struct <anonymous> *}' but argument is of type 'int *'
    static __always_inline int atomic_read(const atomic_t *v)
                               ^~~~~~~~~~~
   In file included from include/linux/mmzone.h:9:0,
                    from include/linux/gfp.h:5,
                    from include/linux/kmod.h:22,
                    from include/linux/module.h:13,
                    from block/blk-core.c:15:

quoted

block/blk-core.c:661:18: error: passing argument 1 of 'atomic_read' from incompatible pointer type [-Werror=incompatible-pointer-types]

        !atomic_read(&q->mq_freeze_depth) ||
                     ^
   include/linux/wait.h:278:7: note: in definition of macro '___wait_event'
      if (condition)      \
          ^~~~~~~~~
   include/linux/wait.h:474:11: note: in expansion of macro '__wait_event_interruptible'
      __ret = __wait_event_interruptible(wq, condition); \
              ^~~~~~~~~~~~~~~~~~~~~~~~~~

quoted

block/blk-core.c:660:9: note: in expansion of macro 'wait_event_interruptible'

      ret = wait_event_interruptible(q->mq_freeze_wq,
            ^~~~~~~~~~~~~~~~~~~~~~~~
   In file included from arch/x86/include/asm/msr.h:66:0,
                    from arch/x86/include/asm/processor.h:20,
                    from arch/x86/include/asm/cpufeature.h:4,
                    from arch/x86/include/asm/thread_info.h:52,
                    from include/linux/thread_info.h:54,
                    from arch/x86/include/asm/preempt.h:6,
                    from include/linux/preempt.h:59,
                    from include/linux/spinlock.h:50,
                    from include/linux/seqlock.h:35,
                    from include/linux/time.h:5,
                    from include/linux/stat.h:18,
                    from include/linux/module.h:10,
                    from block/blk-core.c:15:
   arch/x86/include/asm/atomic.h:24:28: note: expected 'const atomic_t * {aka const struct <anonymous> *}' but argument is of type 'int *'
    static __always_inline int atomic_read(const atomic_t *v)
                               ^~~~~~~~~~~
   cc1: some warnings being treated as errors

vim +/atomic_read +661 block/blk-core.c

3ef28e83 Dan Williams      2015-10-21  654  		if (percpu_ref_tryget_live(&q->q_usage_counter))
3ef28e83 Dan Williams      2015-10-21  655  			return 0;
3ef28e83 Dan Williams      2015-10-21  656  
6f3b0e8b Christoph Hellwig 2015-11-26  657  		if (nowait)
3ef28e83 Dan Williams      2015-10-21  658  			return -EBUSY;
3ef28e83 Dan Williams      2015-10-21  659  
3ef28e83 Dan Williams      2015-10-21 @660  		ret = wait_event_interruptible(q->mq_freeze_wq,
3ef28e83 Dan Williams      2015-10-21 @661  				!atomic_read(&q->mq_freeze_depth) ||
3ef28e83 Dan Williams      2015-10-21  662  				blk_queue_dying(q));
3ef28e83 Dan Williams      2015-10-21  663  		if (blk_queue_dying(q))
3ef28e83 Dan Williams      2015-10-21  664  			return -ENODEV;

:::::: The code at line 661 was first introduced by commit
:::::: 3ef28e83ab15799742e55fd13243a5f678b04242 block: generic request_queue reference counting

:::::: TO: Dan Williams [off-list ref]
:::::: CC: Jens Axboe [off-list ref]

3 more lines

Hi Roman,

[auto build test WARNING on block/for-next]
[also build test WARNING on v4.7 next-20160805]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Roman-Pen/blk-mq-fix-hang-caused-by-freeze-unfreeze-sequence/20160806-014441
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
config: x86_64-randconfig-x012-201631 (attached as .config)
compiler: gcc-6 (Debian 6.1.1-9) 6.1.1 20160705
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All warnings (new ones prefixed by >>):

   In file included from include/linux/linkage.h:4:0,
                    from include/linux/kernel.h:6,
                    from block/blk-core.c:14:
   block/blk-core.c: In function 'blk_queue_enter':
   block/blk-core.c:661:18: error: passing argument 1 of 'atomic_read' from incompatible pointer type [-Werror=incompatible-pointer-types]
        !atomic_read(&q->mq_freeze_depth) ||
                     ^
   include/linux/compiler.h:151:30: note: in definition of macro '__trace_if'
     if (__builtin_constant_p(!!(cond)) ? !!(cond) :   \
                                 ^~~~

quoted

include/linux/wait.h:473:2: note: in expansion of macro 'if'

     if (!(condition))      \
     ^~
   block/blk-core.c:660:9: note: in expansion of macro 'wait_event_interruptible'
      ret = wait_event_interruptible(q->mq_freeze_wq,
            ^~~~~~~~~~~~~~~~~~~~~~~~
   In file included from arch/x86/include/asm/msr.h:66:0,
                    from arch/x86/include/asm/processor.h:20,
                    from arch/x86/include/asm/cpufeature.h:4,
                    from arch/x86/include/asm/thread_info.h:52,
                    from include/linux/thread_info.h:54,
                    from arch/x86/include/asm/preempt.h:6,
                    from include/linux/preempt.h:59,
                    from include/linux/spinlock.h:50,
                    from include/linux/seqlock.h:35,
                    from include/linux/time.h:5,
                    from include/linux/stat.h:18,
                    from include/linux/module.h:10,
                    from block/blk-core.c:15:
   arch/x86/include/asm/atomic.h:24:28: note: expected 'const atomic_t * {aka const struct <anonymous> *}' but argument is of type 'int *'
    static __always_inline int atomic_read(const atomic_t *v)
                               ^~~~~~~~~~~
   In file included from include/linux/linkage.h:4:0,
                    from include/linux/kernel.h:6,
                    from block/blk-core.c:14:
   block/blk-core.c:661:18: error: passing argument 1 of 'atomic_read' from incompatible pointer type [-Werror=incompatible-pointer-types]
        !atomic_read(&q->mq_freeze_depth) ||
                     ^
   include/linux/compiler.h:151:42: note: in definition of macro '__trace_if'
     if (__builtin_constant_p(!!(cond)) ? !!(cond) :   \
                                             ^~~~

quoted

include/linux/wait.h:473:2: note: in expansion of macro 'if'

     if (!(condition))      \
     ^~
   block/blk-core.c:660:9: note: in expansion of macro 'wait_event_interruptible'
      ret = wait_event_interruptible(q->mq_freeze_wq,
            ^~~~~~~~~~~~~~~~~~~~~~~~
   In file included from arch/x86/include/asm/msr.h:66:0,
                    from arch/x86/include/asm/processor.h:20,
                    from arch/x86/include/asm/cpufeature.h:4,
                    from arch/x86/include/asm/thread_info.h:52,
                    from include/linux/thread_info.h:54,
                    from arch/x86/include/asm/preempt.h:6,
                    from include/linux/preempt.h:59,
                    from include/linux/spinlock.h:50,
                    from include/linux/seqlock.h:35,
                    from include/linux/time.h:5,
                    from include/linux/stat.h:18,
                    from include/linux/module.h:10,
                    from block/blk-core.c:15:
   arch/x86/include/asm/atomic.h:24:28: note: expected 'const atomic_t * {aka const struct <anonymous> *}' but argument is of type 'int *'
    static __always_inline int atomic_read(const atomic_t *v)
                               ^~~~~~~~~~~
   In file included from include/linux/linkage.h:4:0,
                    from include/linux/kernel.h:6,
                    from block/blk-core.c:14:
   block/blk-core.c:661:18: error: passing argument 1 of 'atomic_read' from incompatible pointer type [-Werror=incompatible-pointer-types]
        !atomic_read(&q->mq_freeze_depth) ||
                     ^
   include/linux/compiler.h:162:16: note: in definition of macro '__trace_if'
      ______r = !!(cond);     \
                   ^~~~

quoted

include/linux/wait.h:473:2: note: in expansion of macro 'if'

     if (!(condition))      \
     ^~
   block/blk-core.c:660:9: note: in expansion of macro 'wait_event_interruptible'
      ret = wait_event_interruptible(q->mq_freeze_wq,
            ^~~~~~~~~~~~~~~~~~~~~~~~
   In file included from arch/x86/include/asm/msr.h:66:0,
                    from arch/x86/include/asm/processor.h:20,
                    from arch/x86/include/asm/cpufeature.h:4,
                    from arch/x86/include/asm/thread_info.h:52,
                    from include/linux/thread_info.h:54,
                    from arch/x86/include/asm/preempt.h:6,
                    from include/linux/preempt.h:59,
                    from include/linux/spinlock.h:50,
                    from include/linux/seqlock.h:35,
                    from include/linux/time.h:5,
                    from include/linux/stat.h:18,
                    from include/linux/module.h:10,
                    from block/blk-core.c:15:
   arch/x86/include/asm/atomic.h:24:28: note: expected 'const atomic_t * {aka const struct <anonymous> *}' but argument is of type 'int *'
    static __always_inline int atomic_read(const atomic_t *v)
                               ^~~~~~~~~~~
   In file included from include/linux/linkage.h:4:0,
                    from include/linux/kernel.h:6,
                    from block/blk-core.c:14:
   block/blk-core.c:661:18: error: passing argument 1 of 'atomic_read' from incompatible pointer type [-Werror=incompatible-pointer-types]
        !atomic_read(&q->mq_freeze_depth) ||
                     ^
   include/linux/compiler.h:151:30: note: in definition of macro '__trace_if'
     if (__builtin_constant_p(!!(cond)) ? !!(cond) :   \
                                 ^~~~
   include/linux/wait.h:278:3: note: in expansion of macro 'if'
      if (condition)      \
      ^~

quoted

include/linux/wait.h:451:2: note: in expansion of macro '___wait_event'

     ___wait_event(wq, condition, TASK_INTERRUPTIBLE, 0, 0,  \
     ^~~~~~~~~~~~~
   include/linux/wait.h:474:11: note: in expansion of macro '__wait_event_interruptible'
      __ret = __wait_event_interruptible(wq, condition); \
              ^~~~~~~~~~~~~~~~~~~~~~~~~~
   block/blk-core.c:660:9: note: in expansion of macro 'wait_event_interruptible'
      ret = wait_event_interruptible(q->mq_freeze_wq,
            ^~~~~~~~~~~~~~~~~~~~~~~~
   In file included from arch/x86/include/asm/msr.h:66:0,
                    from arch/x86/include/asm/processor.h:20,
                    from arch/x86/include/asm/cpufeature.h:4,
                    from arch/x86/include/asm/thread_info.h:52,
                    from include/linux/thread_info.h:54,
                    from arch/x86/include/asm/preempt.h:6,
                    from include/linux/preempt.h:59,
                    from include/linux/spinlock.h:50,
                    from include/linux/seqlock.h:35,
                    from include/linux/time.h:5,
                    from include/linux/stat.h:18,
                    from include/linux/module.h:10,
                    from block/blk-core.c:15:
   arch/x86/include/asm/atomic.h:24:28: note: expected 'const atomic_t * {aka const struct <anonymous> *}' but argument is of type 'int *'
    static __always_inline int atomic_read(const atomic_t *v)
                               ^~~~~~~~~~~
   In file included from include/linux/linkage.h:4:0,
                    from include/linux/kernel.h:6,
                    from block/blk-core.c:14:
   block/blk-core.c:661:18: error: passing argument 1 of 'atomic_read' from incompatible pointer type [-Werror=incompatible-pointer-types]
        !atomic_read(&q->mq_freeze_depth) ||
                     ^
   include/linux/compiler.h:151:42: note: in definition of macro '__trace_if'
     if (__builtin_constant_p(!!(cond)) ? !!(cond) :   \
                                             ^~~~
   include/linux/wait.h:278:3: note: in expansion of macro 'if'
      if (condition)      \
      ^~

quoted

include/linux/wait.h:451:2: note: in expansion of macro '___wait_event'

     ___wait_event(wq, condition, TASK_INTERRUPTIBLE, 0, 0,  \
     ^~~~~~~~~~~~~
   include/linux/wait.h:474:11: note: in expansion of macro '__wait_event_interruptible'
      __ret = __wait_event_interruptible(wq, condition); \
              ^~~~~~~~~~~~~~~~~~~~~~~~~~
   block/blk-core.c:660:9: note: in expansion of macro 'wait_event_interruptible'
      ret = wait_event_interruptible(q->mq_freeze_wq,
            ^~~~~~~~~~~~~~~~~~~~~~~~
   In file included from arch/x86/include/asm/msr.h:66:0,
                    from arch/x86/include/asm/processor.h:20,
                    from arch/x86/include/asm/cpufeature.h:4,
                    from arch/x86/include/asm/thread_info.h:52,
                    from include/linux/thread_info.h:54,
                    from arch/x86/include/asm/preempt.h:6,
                    from include/linux/preempt.h:59,
                    from include/linux/spinlock.h:50,
                    from include/linux/seqlock.h:35,
                    from include/linux/time.h:5,
                    from include/linux/stat.h:18,
                    from include/linux/module.h:10,
                    from block/blk-core.c:15:
   arch/x86/include/asm/atomic.h:24:28: note: expected 'const atomic_t * {aka const struct <anonymous> *}' but argument is of type 'int *'
    static __always_inline int atomic_read(const atomic_t *v)
                               ^~~~~~~~~~~
   In file included from include/linux/linkage.h:4:0,
                    from include/linux/kernel.h:6,
                    from block/blk-core.c:14:
   block/blk-core.c:661:18: error: passing argument 1 of 'atomic_read' from incompatible pointer type [-Werror=incompatible-pointer-types]
        !atomic_read(&q->mq_freeze_depth) ||
                     ^
   include/linux/compiler.h:162:16: note: in definition of macro '__trace_if'
      ______r = !!(cond);     \
                   ^~~~
   include/linux/wait.h:278:3: note: in expansion of macro 'if'
      if (condition)      \
      ^~

quoted

include/linux/wait.h:451:2: note: in expansion of macro '___wait_event'

     ___wait_event(wq, condition, TASK_INTERRUPTIBLE, 0, 0,  \
     ^~~~~~~~~~~~~
   include/linux/wait.h:474:11: note: in expansion of macro '__wait_event_interruptible'
      __ret = __wait_event_interruptible(wq, condition); \
              ^~~~~~~~~~~~~~~~~~~~~~~~~~
   block/blk-core.c:660:9: note: in expansion of macro 'wait_event_interruptible'
      ret = wait_event_interruptible(q->mq_freeze_wq,
            ^~~~~~~~~~~~~~~~~~~~~~~~
   In file included from arch/x86/include/asm/msr.h:66:0,
                    from arch/x86/include/asm/processor.h:20,
                    from arch/x86/include/asm/cpufeature.h:4,
                    from arch/x86/include/asm/thread_info.h:52,
                    from include/linux/thread_info.h:54,
                    from arch/x86/include/asm/preempt.h:6,
                    from include/linux/preempt.h:59,
                    from include/linux/spinlock.h:50,
                    from include/linux/seqlock.h:35,
                    from include/linux/time.h:5,
                    from include/linux/stat.h:18,
                    from include/linux/module.h:10,
                    from block/blk-core.c:15:
   arch/x86/include/asm/atomic.h:24:28: note: expected 'const atomic_t * {aka const struct <anonymous> *}' but argument is of type 'int *'
    static __always_inline int atomic_read(const atomic_t *v)
                               ^~~~~~~~~~~
   cc1: some warnings being treated as errors

vim +/if +473 include/linux/wait.h

41a1431b1 Peter Zijlstra 2013-10-02  272  	else								\
c2d816443 Oleg Nesterov  2013-10-07  273  		__wait.flags = 0;					\
c2d816443 Oleg Nesterov  2013-10-07  274  									\
c2d816443 Oleg Nesterov  2013-10-07  275  	for (;;) {							\
c2d816443 Oleg Nesterov  2013-10-07  276  		long __int = prepare_to_wait_event(&wq, &__wait, state);\
41a1431b1 Peter Zijlstra 2013-10-02  277  									\
41a1431b1 Peter Zijlstra 2013-10-02 @278  		if (condition)						\
41a1431b1 Peter Zijlstra 2013-10-02  279  			break;						\
41a1431b1 Peter Zijlstra 2013-10-02  280  									\
c2d816443 Oleg Nesterov  2013-10-07  281  		if (___wait_is_interruptible(state) && __int) {		\
c2d816443 Oleg Nesterov  2013-10-07  282  			__ret = __int;					\
41a1431b1 Peter Zijlstra 2013-10-02  283  			if (exclusive) {				\

203 more lines

Hi Roman,

[auto build test WARNING on block/for-next]
[also build test WARNING on v4.7 next-20160805]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Roman-Pen/blk-mq-fix-hang-caused-by-freeze-unfreeze-sequence/20160806-014441
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
config: tile-allyesconfig (attached as .config)
compiler: tilegx-linux-gcc (GCC) 4.6.2
reproduce:
        wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=tile 

All warnings (new ones prefixed by >>):

   block/blk-core.c: In function 'blk_queue_enter':

quoted

block/blk-core.c:660:3: warning: passing argument 1 of 'atomic_read' from incompatible pointer type [enabled by default]

   arch/tile/include/asm/atomic.h:35:19: note: expected 'const struct atomic_t *' but argument is of type 'int *'

quoted

block/blk-core.c:660:3: warning: passing argument 1 of 'atomic_read' from incompatible pointer type [enabled by default]

   arch/tile/include/asm/atomic.h:35:19: note: expected 'const struct atomic_t *' but argument is of type 'int *'

vim +/atomic_read +660 block/blk-core.c

^1da177e drivers/block/ll_rw_blk.c Linus Torvalds    2005-04-16  644  {
c304a51b block/blk-core.c          Ezequiel Garcia   2012-11-10  645  	return blk_alloc_queue_node(gfp_mask, NUMA_NO_NODE);
1946089a drivers/block/ll_rw_blk.c Christoph Lameter 2005-06-23  646  }
1946089a drivers/block/ll_rw_blk.c Christoph Lameter 2005-06-23  647  EXPORT_SYMBOL(blk_alloc_queue);
^1da177e drivers/block/ll_rw_blk.c Linus Torvalds    2005-04-16  648  
6f3b0e8b block/blk-core.c          Christoph Hellwig 2015-11-26  649  int blk_queue_enter(struct request_queue *q, bool nowait)
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  650  {
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  651  	while (true) {
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  652  		int ret;
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  653  
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  654  		if (percpu_ref_tryget_live(&q->q_usage_counter))
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  655  			return 0;
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  656  
6f3b0e8b block/blk-core.c          Christoph Hellwig 2015-11-26  657  		if (nowait)
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  658  			return -EBUSY;
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  659  
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21 @660  		ret = wait_event_interruptible(q->mq_freeze_wq,
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  661  				!atomic_read(&q->mq_freeze_depth) ||
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  662  				blk_queue_dying(q));
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  663  		if (blk_queue_dying(q))
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  664  			return -ENODEV;
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  665  		if (ret)
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  666  			return ret;
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  667  	}
3ef28e83 block/blk-core.c          Dan Williams      2015-10-21  668  }

:::::: The code at line 660 was first introduced by commit
:::::: 3ef28e83ab15799742e55fd13243a5f678b04242 block: generic request_queue reference counting

:::::: TO: Dan Williams [off-list ref]
:::::: CC: Jens Axboe [off-list ref]

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