[PATCH v4 0/6] solve deadlock caused by memory allocation with I/O

This patchset try to solve one deadlock problem which might be caused
by memory allocation with block I/O during runtime PM and block device
error handling path. Traditionly, the problem is addressed by passing
GFP_NOIO statically to mm, but that is not a effective solution, see
detailed description in patch 1's commit log.

This patch set introduces one process flag and trys to fix the deadlock
problem on block device/network device during runtime PM or usb bus reset.

The 1st one is the change on include/sched.h and mm.

The 2nd patch introduces the flag of memalloc_noio on 'dev_pm_info',
and pm_runtime_set_memalloc_noio(), so that PM Core can teach mm to not
allocate mm with GFP_IOFS during the runtime_resume callback only on
device with the flag set.

The following 2 patches apply the introduced pm_runtime_set_memalloc_noio()
to mark all devices as memalloc_noio_resume in the path from the block or
network device to the root device in device tree.

The last 2 patches are applied again PM and USB subsystem to demonstrate
how to use the introduced mechanism to fix the deadlock problem.

Change logs:
V4:
	- patches from the 2nd to the 6th changed	
	- call pm_runtime_set_memalloc_noio() after device_add() as pointed
	by Alan
	- set PF_MEMALLOC_NOIO during runtime_suspend()

V3:
        - patch 2/6 and 5/6 changed, see their commit log
        - remove RFC from title since several guys have expressed that
        it is a reasonable solution
V2:
        - remove changes on 'may_writepage' and 'may_swap'(1/6)
        - unset GFP_IOFS in try_to_free_pages() path(1/6)
        - introduce pm_runtime_set_memalloc_noio()
        - only apply the meachnism on block/network device and its ancestors
        for runtime resume context
V1:
        - take Minchan's change to avoid the check in alloc_page hot path
        - change the helpers' style into save/restore as suggested by Alan
        - memory allocation with no io in usb bus reset path for all devices
        as suggested by Greg and Oliver

 block/genhd.c                |    9 +++++
 drivers/base/power/runtime.c |   89 +++++++++++++++++++++++++++++++++++++++++-
 drivers/usb/core/hub.c       |   13 ++++++
 include/linux/pm.h           |    1 +
 include/linux/pm_runtime.h   |    3 ++
 include/linux/sched.h        |   10 +++++
 mm/page_alloc.c              |   10 ++++-
 mm/vmscan.c                  |   12 ++++++
 net/core/net-sysfs.c         |    5 +++


Thanks,
--
Ming Lei

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This patch introduces PF_MEMALLOC_NOIO on process flag('flags' field of
'struct task_struct'), so that the flag can be set by one task
to avoid doing I/O inside memory allocation in the task's context.

The patch trys to solve one deadlock problem caused by block device,
and the problem may happen at least in the below situations:

- during block device runtime resume, if memory allocation with
GFP_KERNEL is called inside runtime resume callback of any one
of its ancestors(or the block device itself), the deadlock may be
triggered inside the memory allocation since it might not complete
until the block device becomes active and the involed page I/O finishes.
The situation is pointed out first by Alan Stern. It is not a good
approach to convert all GFP_KERNEL[1] in the path into GFP_NOIO because
several subsystems may be involved(for example, PCI, USB and SCSI may
be involved for usb mass stoarage device, network devices involved too
in the iSCSI case)

- during block device runtime suspend, because runtime resume need
to wait for completion of concurrent runtime suspend.

- during error handling of usb mass storage deivce, USB bus reset
will be put on the device, so there shouldn't have any
memory allocation with GFP_KERNEL during USB bus reset, otherwise
the deadlock similar with above may be triggered. Unfortunately, any
usb device may include one mass storage interface in theory, so it
requires all usb interface drivers to handle the situation. In fact,
most usb drivers don't know how to handle bus reset on the device
and don't provide .pre_set() and .post_reset() callback at all, so
USB core has to unbind and bind driver for these devices. So it
is still not practical to resort to GFP_NOIO for solving the problem.

Also the introduced solution can be used by block subsystem or block
drivers too, for example, set the PF_MEMALLOC_NOIO flag before doing
actual I/O transfer.

It is not a good idea to convert all these GFP_KERNEL in the
affected path into GFP_NOIO because these functions doing that may be
implemented as library and will be called in many other contexts.

In fact, memalloc_noio() can convert some of current static GFP_NOIO
allocation into GFP_KERNEL back in other non-affected contexts, at least
almost all GFP_NOIO in USB subsystem can be converted into GFP_KERNEL
after applying the approach and make allocation with GFP_IO
only happen in runtime resume/bus reset/block I/O transfer contexts
generally.

[1], several GFP_KERNEL allocation examples in runtime resume path

- pci subsystem
acpi_os_allocate
	<-acpi_ut_allocate
		<-ACPI_ALLOCATE_ZEROED
			<-acpi_evaluate_object
				<-__acpi_bus_set_power
					<-acpi_bus_set_power
						<-acpi_pci_set_power_state
							<-platform_pci_set_power_state
								<-pci_platform_power_transition
									<-__pci_complete_power_transition
										<-pci_set_power_state
											<-pci_restore_standard_config
												<-pci_pm_runtime_resume
- usb subsystem
usb_get_status
	<-finish_port_resume
		<-usb_port_resume
			<-generic_resume
				<-usb_resume_device
					<-usb_resume_both
						<-usb_runtime_resume

- some individual usb drivers
usblp, uvc, gspca, most of dvb-usb-v2 media drivers, cpia2, az6007, ....

That is just what I have found.  Unfortunately, this allocation can
only be found by human being now, and there should be many not found
since any function in the resume path(call tree) may allocate memory
with GFP_KERNEL.

Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Oliver Neukum <redacted>
Cc: Jiri Kosina <redacted>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mel Gorman <redacted>
Cc: KAMEZAWA Hiroyuki <redacted>
Cc: Michal Hocko <redacted>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Rafael J. Wysocki" <redacted>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Ming Lei <redacted>
---
v4:
	- fix comment
v3:
	- no change
v2:
        - remove changes on 'may_writepage' and 'may_swap' because that
          isn't related with the patchset, and can't introduce I/O in
          allocation path if GFP_IOFS is unset, so handing 'may_swap'
          and may_writepage on GFP_NOIO or GFP_NOFS  should be a
          mm internal thing, and let mm guys deal with that, :-).

          Looks clearing the two may_XXX flag only excludes dirty pages
	  	  and anon pages for relaiming, and the behaviour should be decided
          by GFP FLAG, IMO.

        - unset GFP_IOFS in try_to_free_pages() path since
          alloc_page_buffers()
          and dma_alloc_from_contiguous may drop into the path, as
          pointed by KAMEZAWA Hiroyuki
v1:
        - take Minchan's change to avoid the check in alloc_page hot
          path

        - change the helpers' style into save/restore as suggested by
          Alan Stern
---
 include/linux/sched.h |   10 ++++++++++
 mm/page_alloc.c       |   10 +++++++++-
 mm/vmscan.c           |   12 ++++++++++++
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index fb27acd..283fe86 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h

@@ -1805,6 +1805,7 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *
 #define PF_FROZEN	0x00010000	/* frozen for system suspend */
 #define PF_FSTRANS	0x00020000	/* inside a filesystem transaction */
 #define PF_KSWAPD	0x00040000	/* I am kswapd */
+#define PF_MEMALLOC_NOIO 0x00080000	/* Allocating memory without IO involved */
 #define PF_LESS_THROTTLE 0x00100000	/* Throttle me less: I clean memory */
 #define PF_KTHREAD	0x00200000	/* I am a kernel thread */
 #define PF_RANDOMIZE	0x00400000	/* randomize virtual address space */

@@ -1842,6 +1843,15 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *
 #define tsk_used_math(p) ((p)->flags & PF_USED_MATH)
 #define used_math() tsk_used_math(current)
 
+#define memalloc_noio() (current->flags & PF_MEMALLOC_NOIO)
+#define memalloc_noio_save(flag) do { \
+	(flag) = current->flags & PF_MEMALLOC_NOIO; \
+	current->flags |= PF_MEMALLOC_NOIO; \
+} while (0)
+#define memalloc_noio_restore(flag) do { \
+	current->flags = (current->flags & ~PF_MEMALLOC_NOIO) | flag; \
+} while (0)
+
 /*
  * task->jobctl flags
  */

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 45c916b..3c47049 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -2634,10 +2634,18 @@ retry_cpuset:
 	page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, nodemask, order,
 			zonelist, high_zoneidx, alloc_flags,
 			preferred_zone, migratetype);
-	if (unlikely(!page))
+	if (unlikely(!page)) {
+		/*
+		 * Runtime PM, block IO and its error handling path
+		 * can deadlock because I/O on the device might not
+		 * complete.
+		 */
+		if (unlikely(memalloc_noio()))
+			gfp_mask &= ~GFP_IOFS;
 		page = __alloc_pages_slowpath(gfp_mask, order,
 				zonelist, high_zoneidx, nodemask,
 				preferred_zone, migratetype);
+	}
 
 	trace_mm_page_alloc(page, order, gfp_mask, migratetype);
 

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 10090c8..035088a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c

@@ -2304,6 +2304,12 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
 		.gfp_mask = sc.gfp_mask,
 	};
 
+	if (unlikely(memalloc_noio())) {
+		gfp_mask &= ~GFP_IOFS;
+		sc.gfp_mask = gfp_mask;
+		shrink.gfp_mask = sc.gfp_mask;
+	}
+
 	throttle_direct_reclaim(gfp_mask, zonelist, nodemask);
 
 	/*

@@ -3304,6 +3310,12 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
 	};
 	unsigned long nr_slab_pages0, nr_slab_pages1;
 
+	if (unlikely(memalloc_noio())) {
+		gfp_mask &= ~GFP_IOFS;
+		sc.gfp_mask = gfp_mask;
+		shrink.gfp_mask = sc.gfp_mask;
+	}
+
 	cond_resched();
 	/*
 	 * We need to be able to allocate from the reserves for RECLAIM_SWAP

-- 
1.7.9.5

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The patch introduces the flag of memalloc_noio in 'struct dev_pm_info'
to help PM core to teach mm not allocating memory with GFP_KERNEL
flag for avoiding probable deadlock.

As explained in the comment, any GFP_KERNEL allocation inside
runtime_resume() or runtime_suspend() on any one of device in
the path from one block or network device to the root device
in the device tree may cause deadlock, the introduced
pm_runtime_set_memalloc_noio() sets or clears the flag on
device in the path recursively.

Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: "Rafael J. Wysocki" <redacted>
Signed-off-by: Ming Lei <redacted>
---
v4:
	- rename memalloc_noio_resume as memalloc_noio
	- remove pm_runtime_get_memalloc_noio()
	- add comments on pm_runtime_set_memalloc_noio
v3:
	- introduce pm_runtime_get_memalloc_noio()
	- hold one global lock on pm_runtime_set_memalloc_noio
	- hold device power lock when accessing memalloc_noio_resume
	  flag suggested by Alan Stern
	- implement pm_runtime_set_memalloc_noio without recursion
	  suggested by Alan Stern
v2:
	- introduce pm_runtime_set_memalloc_noio()
---
 drivers/base/power/runtime.c |   57 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/pm.h           |    1 +
 include/linux/pm_runtime.h   |    3 +++
 3 files changed, 61 insertions(+)

diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index 3148b10..d477924 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c

@@ -124,6 +124,63 @@ unsigned long pm_runtime_autosuspend_expiration(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(pm_runtime_autosuspend_expiration);
 
+static int dev_memalloc_noio(struct device *dev, void *data)
+{
+	return dev->power.memalloc_noio;
+}
+
+/*
+ * pm_runtime_set_memalloc_noio - Set a device's memalloc_noio flag.
+ * @dev: Device to handle.
+ * @enable: True for setting the flag and False for clearing the flag.
+ *
+ * Set the flag for all devices in the path from the device to the
+ * root device in the device tree if @enable is true, otherwise clear
+ * the flag for devices in the path whose siblings don't set the flag.
+ *
+ * The function should only be called by block device, or network
+ * device driver for solving the deadlock problem during runtime
+ * resume/suspend:
+ * 	if memory allocation with GFP_KERNEL is called inside runtime
+ * 	resume/suspend callback of any one of its ancestors(or the
+ * 	block device itself), the deadlock may be triggered inside the
+ * 	memory allocation since it might not complete until the block
+ * 	device becomes active and the involed page I/O finishes. The
+ * 	situation is pointed out first by Alan Stern. Network device
+ * 	are involved in iSCSI kind of situation.
+ *
+ * The lock of dev_hotplug_mutex is held in the function for handling
+ * hotplug race because pm_runtime_set_memalloc_noio() may be called
+ * in async probe().
+ *
+ * The function should be called between device_add() and device_del()
+ * on the affected device(block/network device).
+ */
+void pm_runtime_set_memalloc_noio(struct device *dev, bool enable)
+{
+	static DEFINE_MUTEX(dev_hotplug_mutex);
+
+	mutex_lock(&dev_hotplug_mutex);
+	for(;;) {
+		/* hold power lock since bitfield is not SMP-safe. */
+		spin_lock_irq(&dev->power.lock);
+		dev->power.memalloc_noio = enable;
+		spin_unlock_irq(&dev->power.lock);
+
+		dev = dev->parent;
+
+		/* only clear the flag for one device if all
+		 * children of the device don't set the flag.
+		 */
+		if (!dev || (!enable &&
+			     device_for_each_child(dev, NULL,
+						   dev_memalloc_noio)))
+			break;
+	}
+	mutex_unlock(&dev_hotplug_mutex);
+}
+EXPORT_SYMBOL_GPL(pm_runtime_set_memalloc_noio);
+
 /**
  * rpm_check_suspend_allowed - Test whether a device may be suspended.
  * @dev: Device to test.

diff --git a/include/linux/pm.h b/include/linux/pm.h
index 03d7bb1..1a8a69d 100644
--- a/include/linux/pm.h
+++ b/include/linux/pm.h

@@ -538,6 +538,7 @@ struct dev_pm_info {
 	unsigned int		irq_safe:1;
 	unsigned int		use_autosuspend:1;
 	unsigned int		timer_autosuspends:1;
+	unsigned int		memalloc_noio:1;
 	enum rpm_request	request;
 	enum rpm_status		runtime_status;
 	int			runtime_error;

diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
index f271860..775e063 100644
--- a/include/linux/pm_runtime.h
+++ b/include/linux/pm_runtime.h

@@ -47,6 +47,7 @@ extern void pm_runtime_set_autosuspend_delay(struct device *dev, int delay);
 extern unsigned long pm_runtime_autosuspend_expiration(struct device *dev);
 extern void pm_runtime_update_max_time_suspended(struct device *dev,
 						 s64 delta_ns);
+extern void pm_runtime_set_memalloc_noio(struct device *dev, bool enable);
 
 static inline bool pm_children_suspended(struct device *dev)
 {

@@ -149,6 +150,8 @@ static inline void pm_runtime_set_autosuspend_delay(struct device *dev,
 						int delay) {}
 static inline unsigned long pm_runtime_autosuspend_expiration(
 				struct device *dev) { return 0; }
+static inline void pm_runtime_set_memalloc_noio(struct device *dev,
+						bool enable){}
 
 #endif /* !CONFIG_PM_RUNTIME */
 

-- 
1.7.9.5

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This patch applyes the introduced pm_runtime_set_memalloc_noio on
block device so that PM core will teach mm to not allocate memory with
GFP_IOFS when calling the runtime_resume and runtime_suspend callback
for block devices and its ancestors.

Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Ming Lei <redacted>
---
v4:
	- call pm_runtime_set_memalloc_noio(ddev, true) after device_add
---
 block/genhd.c |    9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/block/genhd.c b/block/genhd.c
index 9e02cd6..f3fe3aa 100644
--- a/block/genhd.c
+++ b/block/genhd.c

@@ -18,6 +18,7 @@
 #include <linux/mutex.h>
 #include <linux/idr.h>
 #include <linux/log2.h>
+#include <linux/pm_runtime.h>
 
 #include "blk.h"
 

@@ -532,6 +533,13 @@ static void register_disk(struct gendisk *disk)
 			return;
 		}
 	}
+
+	/* avoid probable deadlock caused by allocating memory with
+	 * GFP_KERNEL in runtime_resume callback of its all ancestor
+	 * deivces
+	 */
+	pm_runtime_set_memalloc_noio(ddev, true);
+
 	disk->part0.holder_dir = kobject_create_and_add("holders", &ddev->kobj);
 	disk->slave_dir = kobject_create_and_add("slaves", &ddev->kobj);
 

@@ -661,6 +669,7 @@ void del_gendisk(struct gendisk *disk)
 	disk->driverfs_dev = NULL;
 	if (!sysfs_deprecated)
 		sysfs_remove_link(block_depr, dev_name(disk_to_dev(disk)));
+	pm_runtime_set_memalloc_noio(disk_to_dev(disk), false);
 	device_del(disk_to_dev(disk));
 }
 EXPORT_SYMBOL(del_gendisk);

-- 
1.7.9.5

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Deadlock might be caused by allocating memory with GFP_KERNEL in
runtime_resume and runtime_suspend callback of network devices in
iSCSI situation, so mark network devices and its ancestor as
'memalloc_noio' with the introduced pm_runtime_set_memalloc_noio().

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <redacted>
Cc: David Decotigny <redacted>
Cc: Tom Herbert <redacted>
Cc: Ingo Molnar <redacted>
Signed-off-by: Ming Lei <redacted>
---
v4:
	 - call pm_runtime_set_memalloc_noio(ddev, true) after
	   device_add
---
 net/core/net-sysfs.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index bcf02f6..a55d255 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c

@@ -22,6 +22,7 @@
 #include <linux/vmalloc.h>
 #include <linux/export.h>
 #include <linux/jiffies.h>
+#include <linux/pm_runtime.h>
 #include <net/wext.h>
 
 #include "net-sysfs.h"

@@ -1386,6 +1387,8 @@ void netdev_unregister_kobject(struct net_device * net)
 
 	remove_queue_kobjects(net);
 
+	pm_runtime_set_memalloc_noio(dev, false);
+
 	device_del(dev);
 }
 

@@ -1421,6 +1424,8 @@ int netdev_register_kobject(struct net_device *net)
 		return error;
 	}
 
+	pm_runtime_set_memalloc_noio(dev, true);
+
 	return error;
 }
 

-- 
1.7.9.5

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This patch applies the introduced memalloc_noio_save() and
memalloc_noio_restore() to force memory allocation with no I/O
during runtime_resume/runtime_suspend callback on device with
the flag of 'memalloc_noio' set.

Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Oliver Neukum <redacted>
Cc: Rafael J. Wysocki <redacted>
Signed-off-by: Ming Lei <redacted>
---
v4:
	- runtime_suspend need this too because rpm_resume may wait for
	completion of concurrent runtime_suspend, so deadlock still may
	be triggered in runtime_suspend path.
---
 drivers/base/power/runtime.c |   32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index d477924..7ed17a9 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c

@@ -368,6 +368,7 @@ static int rpm_suspend(struct device *dev, int rpmflags)
 	int (*callback)(struct device *);
 	struct device *parent = NULL;
 	int retval;
+	unsigned int noio_flag;
 
 	trace_rpm_suspend(dev, rpmflags);
 

@@ -477,7 +478,20 @@ static int rpm_suspend(struct device *dev, int rpmflags)
 	if (!callback && dev->driver && dev->driver->pm)
 		callback = dev->driver->pm->runtime_suspend;
 
-	retval = rpm_callback(callback, dev);
+	/*
+	 * Deadlock might be caused if memory allocation with GFP_KERNEL
+	 * happens inside runtime_suspend callback of one block device's
+	 * ancestor or the block device itself. Network device might be
+	 * thought as part of iSCSI block device, so network device and
+	 * its ancestor should be marked as memalloc_noio.
+	 */
+	if (dev->power.memalloc_noio) {
+		memalloc_noio_save(noio_flag);
+		retval = rpm_callback(callback, dev);
+		memalloc_noio_restore(noio_flag);
+	} else {
+		retval = rpm_callback(callback, dev);
+	}
 	if (retval)
 		goto fail;
 

@@ -560,6 +574,7 @@ static int rpm_resume(struct device *dev, int rpmflags)
 	int (*callback)(struct device *);
 	struct device *parent = NULL;
 	int retval = 0;
+	unsigned int noio_flag;
 
 	trace_rpm_resume(dev, rpmflags);
 

@@ -709,7 +724,20 @@ static int rpm_resume(struct device *dev, int rpmflags)
 	if (!callback && dev->driver && dev->driver->pm)
 		callback = dev->driver->pm->runtime_resume;
 
-	retval = rpm_callback(callback, dev);
+	/*
+	 * Deadlock might be caused if memory allocation with GFP_KERNEL
+	 * happens inside runtime_resume callback of one block device's
+	 * ancestor or the block device itself. Network device might be
+	 * thought as part of iSCSI block device, so network device and
+	 * its ancestor should be marked as memalloc_noio.
+	 */
+	if (dev->power.memalloc_noio) {
+		memalloc_noio_save(noio_flag);
+		retval = rpm_callback(callback, dev);
+		memalloc_noio_restore(noio_flag);
+	} else {
+		retval = rpm_callback(callback, dev);
+	}
 	if (retval) {
 		__update_runtime_status(dev, RPM_SUSPENDED);
 		pm_runtime_cancel_pending(dev);

-- 
1.7.9.5

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If one storage interface or usb network interface(iSCSI case)
exists in current configuration, memory allocation with
GFP_KERNEL during usb_device_reset() might trigger I/O transfer
on the storage interface itself and cause deadlock because
the 'us->dev_mutex' is held in .pre_reset() and the storage
interface can't do I/O transfer when the reset is triggered
by other interface, or the error handling can't be completed
if the reset is triggered by the storage itself(error handling path).

Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Oliver Neukum <redacted>
Signed-off-by: Ming Lei <redacted>
---
v4:
	- mark current memalloc_noio for every usb device reset
---
 drivers/usb/core/hub.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 5b131b6..788e652 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c

@@ -5044,6 +5044,7 @@ int usb_reset_device(struct usb_device *udev)
 {
 	int ret;
 	int i;
+	unsigned int noio_flag;
 	struct usb_host_config *config = udev->actconfig;
 
 	if (udev->state == USB_STATE_NOTATTACHED ||

@@ -5053,6 +5054,17 @@ int usb_reset_device(struct usb_device *udev)
 		return -EINVAL;
 	}
 
+	/*
+	 * Don't allocate memory with GFP_KERNEL in current
+	 * context to avoid possible deadlock if usb mass
+	 * storage interface or usbnet interface(iSCSI case)
+	 * is included in current configuration. The easist
+	 * approach is to do it for every device reset,
+	 * because the device 'memalloc_noio' flag may have
+	 * not been set before reseting the usb device.
+	 */
+	memalloc_noio_save(noio_flag);
+
 	/* Prevent autosuspend during the reset */
 	usb_autoresume_device(udev);
 

@@ -5097,6 +5109,7 @@ int usb_reset_device(struct usb_device *udev)
 	}
 
 	usb_autosuspend_device(udev);
+	memalloc_noio_restore(noio_flag);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(usb_reset_device);

-- 
1.7.9.5

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On Sat,  3 Nov 2012 16:35:08 +0800
Ming Lei [off-list ref] wrote:

This patchset try to solve one deadlock problem which might be caused
by memory allocation with block I/O during runtime PM and block device
error handling path. Traditionly, the problem is addressed by passing
GFP_NOIO statically to mm, but that is not a effective solution, see
detailed description in patch 1's commit log.

It generally looks OK to me.  I have a few comments and I expect to grab
v5.

Rafael, your thoughts?

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On Sat,  3 Nov 2012 16:35:09 +0800
Ming Lei [off-list ref] wrote:

This patch introduces PF_MEMALLOC_NOIO on process flag('flags' field of
'struct task_struct'), so that the flag can be set by one task
to avoid doing I/O inside memory allocation in the task's context.

The patch trys to solve one deadlock problem caused by block device,
and the problem may happen at least in the below situations:

- during block device runtime resume, if memory allocation with
GFP_KERNEL is called inside runtime resume callback of any one
of its ancestors(or the block device itself), the deadlock may be
triggered inside the memory allocation since it might not complete
until the block device becomes active and the involed page I/O finishes.
The situation is pointed out first by Alan Stern. It is not a good
approach to convert all GFP_KERNEL[1] in the path into GFP_NOIO because
several subsystems may be involved(for example, PCI, USB and SCSI may
be involved for usb mass stoarage device, network devices involved too
in the iSCSI case)

- during block device runtime suspend, because runtime resume need
to wait for completion of concurrent runtime suspend.

- during error handling of usb mass storage deivce, USB bus reset
will be put on the device, so there shouldn't have any
memory allocation with GFP_KERNEL during USB bus reset, otherwise
the deadlock similar with above may be triggered. Unfortunately, any
usb device may include one mass storage interface in theory, so it
requires all usb interface drivers to handle the situation. In fact,
most usb drivers don't know how to handle bus reset on the device
and don't provide .pre_set() and .post_reset() callback at all, so
USB core has to unbind and bind driver for these devices. So it
is still not practical to resort to GFP_NOIO for solving the problem.

Also the introduced solution can be used by block subsystem or block
drivers too, for example, set the PF_MEMALLOC_NOIO flag before doing
actual I/O transfer.

It is not a good idea to convert all these GFP_KERNEL in the
affected path into GFP_NOIO because these functions doing that may be
implemented as library and will be called in many other contexts.

In fact, memalloc_noio() can convert some of current static GFP_NOIO
allocation into GFP_KERNEL back in other non-affected contexts, at least
almost all GFP_NOIO in USB subsystem can be converted into GFP_KERNEL
after applying the approach and make allocation with GFP_IO
only happen in runtime resume/bus reset/block I/O transfer contexts
generally.

It's unclear from the description why we're also clearing __GFP_FS in
this situation.

If we can avoid doing this then there will be a very small gain: there
are some situations in which a filesystem can clean pagecache without
performing I/O.


It doesn't appear that the patch will add overhead to the alloc/free
hotpaths, which is good.

Again with the ghastly macros.  Please, do this properly in regular old
C, as previously discussed.  It really doesn't matter what daft things
local_irq_save() did 20 years ago.  Just do it right!

Also, you can probably put the unlikely() inside memalloc_noio() and
avoid repeating it at all the callsites.

And it might be neater to do:

/*
 * Nice comment goes here
 */
static inline gfp_t memalloc_noio_flags(gfp_t flags)
{
	if (unlikely(current->flags & PF_MEMALLOC_NOIO))
		flags &= ~GFP_IOFS;
	return flags;
}

We can avoid writing to shrink.gfp_mask twice.  And maybe sc.gfp_mask
as well.  Unclear, I didn't think about it too hard ;)

 	throttle_direct_reclaim(gfp_mask, zonelist, nodemask);
 
 	/*

...

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On Sat,  3 Nov 2012 16:35:10 +0800
Ming Lei [off-list ref] wrote:

The patch introduces the flag of memalloc_noio in 'struct dev_pm_info'
to help PM core to teach mm not allocating memory with GFP_KERNEL
flag for avoiding probable deadlock.

As explained in the comment, any GFP_KERNEL allocation inside
runtime_resume() or runtime_suspend() on any one of device in
the path from one block or network device to the root device
in the device tree may cause deadlock, the introduced
pm_runtime_set_memalloc_noio() sets or clears the flag on
device in the path recursively.

checkpatch finds a number of problems with this patch, all of which
should be fixed.  Please always use checkpatch.

Such a comment is usually laid out as

		/*
		 * Only ...

More significantly, the comment describes what the code is doing but
not why the code is doing it.  The former is (usually) obvious from
reading the C, and the latter is what good code comments address.

And it's needed in this case.  Why does the code do this?

Also, can a device have more than one child?  If so, the code doesn't
do what the comment says it does.

+		if (!dev || (!enable &&
+			     device_for_each_child(dev, NULL,
+						   dev_memalloc_noio)))
+			break;
+	}
+	mutex_unlock(&dev_hotplug_mutex);
+}
+EXPORT_SYMBOL_GPL(pm_runtime_set_memalloc_noio);

...

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On Sat,  3 Nov 2012 16:35:11 +0800
Ming Lei [off-list ref] wrote:

Again, please fix the comment style.  Take a look at the rest of this file!

+	 * GFP_KERNEL in runtime_resume callback of its all ancestor
+	 * deivces

typo

+	 */

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On Wed, Nov 7, 2012 at 7:23 AM, Andrew Morton [off-list ref] wrote:

It's unclear from the description why we're also clearing __GFP_FS in
this situation.

If we can avoid doing this then there will be a very small gain: there
are some situations in which a filesystem can clean pagecache without
performing I/O.

Firstly,  the patch follows the policy in the system suspend/resume situation,
in which the __GFP_FS is cleared, and basically the problem is very similar
with that in system PM path.

Secondly, inside shrink_page_list(), pageout() may be triggered on dirty anon
page if __GFP_FS is set.

IMO, if performing I/O can be completely avoided when __GFP_FS is set, the
flag can be kept, otherwise it is better to clear it in the situation.

It doesn't appear that the patch will add overhead to the alloc/free
hotpaths, which is good.

Thanks for previous Minchan's comment.

quoted

...

--- a/include/linux/sched.h
+++ b/include/linux/sched.h

@@ -1805,6 +1805,7 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *
 #define PF_FROZEN    0x00010000      /* frozen for system suspend */
 #define PF_FSTRANS   0x00020000      /* inside a filesystem transaction */
 #define PF_KSWAPD    0x00040000      /* I am kswapd */
+#define PF_MEMALLOC_NOIO 0x00080000  /* Allocating memory without IO involved */
 #define PF_LESS_THROTTLE 0x00100000  /* Throttle me less: I clean memory */
 #define PF_KTHREAD   0x00200000      /* I am a kernel thread */
 #define PF_RANDOMIZE 0x00400000      /* randomize virtual address space */

@@ -1842,6 +1843,15 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *
 #define tsk_used_math(p) ((p)->flags & PF_USED_MATH)
 #define used_math() tsk_used_math(current)

+#define memalloc_noio() (current->flags & PF_MEMALLOC_NOIO)
+#define memalloc_noio_save(flag) do { \
+     (flag) = current->flags & PF_MEMALLOC_NOIO; \
+     current->flags |= PF_MEMALLOC_NOIO; \
+} while (0)
+#define memalloc_noio_restore(flag) do { \
+     current->flags = (current->flags & ~PF_MEMALLOC_NOIO) | flag; \
+} while (0)
+

Again with the ghastly macros.  Please, do this properly in regular old
C, as previously discussed.  It really doesn't matter what daft things
local_irq_save() did 20 years ago.  Just do it right!

OK, I will take inline function in -v5.

Also, you can probably put the unlikely() inside memalloc_noio() and
avoid repeating it at all the callsites.

And it might be neater to do:

/*
 * Nice comment goes here
 */
static inline gfp_t memalloc_noio_flags(gfp_t flags)
{
        if (unlikely(current->flags & PF_MEMALLOC_NOIO))
                flags &= ~GFP_IOFS;
        return flags;
}

But without the check in callsites, some local variables will be write
two times,
so it is better to not do it.

quoted

  * task->jobctl flags
  */

...

@@ -2304,6 +2304,12 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
              .gfp_mask = sc.gfp_mask,
      };

+     if (unlikely(memalloc_noio())) {
+             gfp_mask &= ~GFP_IOFS;
+             sc.gfp_mask = gfp_mask;
+             shrink.gfp_mask = sc.gfp_mask;
+     }

We can avoid writing to shrink.gfp_mask twice.  And maybe sc.gfp_mask
as well.  Unclear, I didn't think about it too hard ;)

Yes, we can do it by initializing 'shrink' local variable just after the branch,
so one writing is enough. Will do it in -v5.

Thanks,
--
Ming Lei

On Wed, Nov 7, 2012 at 7:24 AM, Andrew Morton [off-list ref] wrote:

checkpatch finds a number of problems with this patch, all of which
should be fixed.  Please always use checkpatch.

Sorry for missing the check.

quoted

+             /* only clear the flag for one device if all
+              * children of the device don't set the flag.
+              */

Such a comment is usually laid out as

                /*
                 * Only ...

Will do it in -v5.

More significantly, the comment describes what the code is doing but
not why the code is doing it.  The former is (usually) obvious from
reading the C, and the latter is what good code comments address.

And it's needed in this case.  Why does the code do this?

Suppose both two usb scsi disks which share the same usb
configuration(device) set the device memalloc_noio flag, and
its ancestors' memalloc_noio flag should be cleared only after
both the two usb scsi disk's flags have been cleared.

OK, we'll add comment on clearing flag.

Also, can a device have more than one child?  If so, the code doesn't
do what the comment says it does.

It should do that because device_for_each_child() returns true immediately
only if dev_memalloc_noio() for one child returns true.

quoted

+             if (!dev || (!enable &&
+                          device_for_each_child(dev, NULL,
+                                                dev_memalloc_noio)))
+                     break;
+     }
+     mutex_unlock(&dev_hotplug_mutex);
+}
+EXPORT_SYMBOL_GPL(pm_runtime_set_memalloc_noio);

Thanks,
--
Ming Lei

On Wed, Nov 7, 2012 at 7:23 AM, Andrew Morton [off-list ref] wrote:

It generally looks OK to me.  I have a few comments and I expect to grab
v5.

Andrew, thanks for your review, and I will prepare -v5 later.

Thanks,
--
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On Wed, 7 Nov 2012 11:11:24 +0800 Ming Lei [off-list ref] wrote:

On Wed, Nov 7, 2012 at 7:23 AM, Andrew Morton [off-list ref] wrote:

quoted

It's unclear from the description why we're also clearing __GFP_FS in
this situation.

If we can avoid doing this then there will be a very small gain: there
are some situations in which a filesystem can clean pagecache without
performing I/O.

Firstly,  the patch follows the policy in the system suspend/resume situation,
in which the __GFP_FS is cleared, and basically the problem is very similar
with that in system PM path.

I suspect that code is wrong.  Or at least, suboptimal.

Secondly, inside shrink_page_list(), pageout() may be triggered on dirty anon
page if __GFP_FS is set.

pageout() should be called if GFP_FS is set or if GFP_IO is set and the
IO is against swap.

And that's what we want to happen: we want to enter the fs to try to
turn dirty pagecache into clean pagecache without doing IO.  If we in
fact enter the device drivers when GFP_IO was not set then that's a bug
which we should fix.

IMO, if performing I/O can be completely avoided when __GFP_FS is set, the
flag can be kept, otherwise it is better to clear it in the situation.

yup.

quoted

Also, you can probably put the unlikely() inside memalloc_noio() and
avoid repeating it at all the callsites.

And it might be neater to do:

/*
 * Nice comment goes here
 */
static inline gfp_t memalloc_noio_flags(gfp_t flags)
{
        if (unlikely(current->flags & PF_MEMALLOC_NOIO))
                flags &= ~GFP_IOFS;
        return flags;
}

But without the check in callsites, some local variables will be write
two times,
so it is better to not do it.

I don't see why - we just modify the incoming gfp_t at the start of the
function, then use it.

It gets a bit tricky with those struct initialisations.  Things like

	struct foo bar {
		.a = a1,
		.b = b1,
	};

should not be turned into

	struct foo bar {
		.a = a1,
	};
	
	bar.b = b1;

and we don't want to do

	struct foo bar { };

	bar.a = a1;
	bar.b = b1;

either, because these are indeed a double-write.  But we can do

	struct foo bar {
		.flags = (flags = memalloc_noio_flags(flags)),
		.b = b1,
	};

which is a bit arcane but not toooo bad.  Have a think about it...


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On Wed, Nov 7, 2012 at 11:48 AM, Andrew Morton
[off-list ref] wrote:

quoted

Firstly,  the patch follows the policy in the system suspend/resume situation,
in which the __GFP_FS is cleared, and basically the problem is very similar
with that in system PM path.

I suspect that code is wrong.  Or at least, suboptimal.

quoted

Secondly, inside shrink_page_list(), pageout() may be triggered on dirty anon
page if __GFP_FS is set.

pageout() should be called if GFP_FS is set or if GFP_IO is set and the
IO is against swap.

And that's what we want to happen: we want to enter the fs to try to
turn dirty pagecache into clean pagecache without doing IO.  If we in
fact enter the device drivers when GFP_IO was not set then that's a bug
which we should fix.

OK, I got it, and I'll not clear GFP_FS in -v5.

quoted

IMO, if performing I/O can be completely avoided when __GFP_FS is set, the
flag can be kept, otherwise it is better to clear it in the situation.

yup.

quoted

quoted

Also, you can probably put the unlikely() inside memalloc_noio() and
avoid repeating it at all the callsites.

And it might be neater to do:

/*
 * Nice comment goes here
 */
static inline gfp_t memalloc_noio_flags(gfp_t flags)
{
        if (unlikely(current->flags & PF_MEMALLOC_NOIO))
                flags &= ~GFP_IOFS;
        return flags;
}

But without the check in callsites, some local variables will be write
two times,
so it is better to not do it.

I don't see why - we just modify the incoming gfp_t at the start of the
function, then use it.

It gets a bit tricky with those struct initialisations.  Things like

        struct foo bar {
                .a = a1,
                .b = b1,
        };

should not be turned into

        struct foo bar {
                .a = a1,
        };

        bar.b = b1;

and we don't want to do

        struct foo bar { };

        bar.a = a1;
        bar.b = b1;

either, because these are indeed a double-write.  But we can do

        struct foo bar {
                .flags = (flags = memalloc_noio_flags(flags)),
                .b = b1,
        };

which is a bit arcane but not toooo bad.  Have a think about it...

Got it, looks memalloc_noio_flags() neater, and I will take it in v5.

Thanks,
--
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