Patch "PM / runtime: Avoid false-positive warnings from might_sleep_if()" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

PM / runtime: Avoid false-positive warnings from might_sleep_if()

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
pm-runtime-avoid-false-positive-warnings-from-might_sleep_if.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Rafael J. Wysocki" <[email protected]>
Date: Tue, 23 May 2017 21:53:54 -0400
Subject: PM / runtime: Avoid false-positive warnings from might_sleep_if()

From: "Rafael J. Wysocki" <[email protected]>

[ Upstream commit a9306a63631493afc75893a4ac405d4e1cbae6aa ]

The might_sleep_if() assertions in __pm_runtime_idle(), __pm_runtime_suspend() and __pm_runtime_resume() may generate false-positive warnings in some situations. For example, that happens if a nested pm_runtime_get_sync()/pm_runtime_put() pair is executed with disabled interrupts within an outer pm_runtime_get_sync()/pm_runtime_put() section for the same device. [Generally, pm_runtime_get_sync() may sleep, so it should not be called with disabled interrupts, but in this particular case the previous pm_runtime_get_sync() guarantees that the device will not be suspended, so the inner pm_runtime_get_sync() will return immediately after incrementing the device's usage counter.]

That started to happen in the i915 driver in 4.10-rc, leading to the following splat:

 BUG: sleeping function called from invalid context at drivers/base/power/runtime.c:1032
 in_atomic(): 1, irqs_disabled(): 0, pid: 1500, name: Xorg
 1 lock held by Xorg/1500:
  #0:  (&dev->struct_mutex){+.+.+.}, at:
  [<ffffffffa0680c13>] i915_mutex_lock_interruptible+0x43/0x140 [i915]
 CPU: 0 PID: 1500 Comm: Xorg Not tainted
 Call Trace:
  dump_stack+0x85/0xc2
  ___might_sleep+0x196/0x260
  __might_sleep+0x53/0xb0
  __pm_runtime_resume+0x7a/0x90
  intel_runtime_pm_get+0x25/0x90 [i915]
  aliasing_gtt_bind_vma+0xaa/0xf0 [i915]
  i915_vma_bind+0xaf/0x1e0 [i915]
  i915_gem_execbuffer_relocate_entry+0x513/0x6f0 [i915]
  i915_gem_execbuffer_relocate_vma.isra.34+0x188/0x250 [i915]
  ? trace_hardirqs_on+0xd/0x10
  ? i915_gem_execbuffer_reserve_vma.isra.31+0x152/0x1f0 [i915]
  ? i915_gem_execbuffer_reserve.isra.32+0x372/0x3a0 [i915]
  i915_gem_do_execbuffer.isra.38+0xa70/0x1a40 [i915]
  ? __might_fault+0x4e/0xb0
  i915_gem_execbuffer2+0xc5/0x260 [i915]
  ? __might_fault+0x4e/0xb0
  drm_ioctl+0x206/0x450 [drm]
  ? i915_gem_execbuffer+0x340/0x340 [i915]
  ? __fget+0x5/0x200
  do_vfs_ioctl+0x91/0x6f0
  ? __fget+0x111/0x200
  ? __fget+0x5/0x200
  SyS_ioctl+0x79/0x90
  entry_SYSCALL_64_fastpath+0x23/0xc6

even though the code triggering it is correct.

Unfortunately, the might_sleep_if() assertions in question are too coarse-grained to cover such cases correctly, so make them a bit less sensitive in order to avoid the false-positives.

---
 drivers/base/power/runtime.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

@@ -889,13 +889,13 @@ int __pm_runtime_idle(struct device *dev
 	unsigned long flags;
 	int retval;
 
-	might_sleep_if(!(rpmflags & RPM_ASYNC) && !dev->power.irq_safe);
-
 	if (rpmflags & RPM_GET_PUT) {
 		if (!atomic_dec_and_test(&dev->power.usage_count))
 			return 0;
 	}
 
+	might_sleep_if(!(rpmflags & RPM_ASYNC) && !dev->power.irq_safe);
+
 	spin_lock_irqsave(&dev->power.lock, flags);
 	retval = rpm_idle(dev, rpmflags);
 	spin_unlock_irqrestore(&dev->power.lock, flags);

@@ -921,13 +921,13 @@ int __pm_runtime_suspend(struct device *
 	unsigned long flags;
 	int retval;
 
-	might_sleep_if(!(rpmflags & RPM_ASYNC) && !dev->power.irq_safe);
-
 	if (rpmflags & RPM_GET_PUT) {
 		if (!atomic_dec_and_test(&dev->power.usage_count))
 			return 0;
 	}
 
+	might_sleep_if(!(rpmflags & RPM_ASYNC) && !dev->power.irq_safe);
+
 	spin_lock_irqsave(&dev->power.lock, flags);
 	retval = rpm_suspend(dev, rpmflags);
 	spin_unlock_irqrestore(&dev->power.lock, flags);

@@ -952,7 +952,8 @@ int __pm_runtime_resume(struct device *d
 	unsigned long flags;
 	int retval;
 
-	might_sleep_if(!(rpmflags & RPM_ASYNC) && !dev->power.irq_safe);
+	might_sleep_if(!(rpmflags & RPM_ASYNC) && !dev->power.irq_safe &&
+			dev->power.runtime_status != RPM_ACTIVE);
 
 	if (rpmflags & RPM_GET_PUT)
 		atomic_inc(&dev->power.usage_count);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/pm-runtime-avoid-false-positive-warnings-from-might_sleep_if.patch