Patch "PM / sleep: don't suspend parent when async child suspend_{noirq, late} fails" 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 / sleep: don't suspend parent when async child suspend_{noirq, late} fails

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-sleep-don-t-suspend-parent-when-async-child-suspend_-noirq-late-fails.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: Brian Norris <[email protected]>
Date: Wed, 9 Nov 2016 17:21:08 -0800
Subject: PM / sleep: don't suspend parent when async child suspend_{noirq, late} fails

From: Brian Norris <[email protected]>

commit 6f75c3fd56daf547d684127a7f83c283c3c160d1 upstream.

Consider two devices, A and B, where B is a child of A, and B utilizes asynchronous suspend (it does not matter whether A is sync or async). If B fails to suspend_noirq() or suspend_late(), or is interrupted by a wakeup (pm_wakeup_pending()), then it aborts and sets the async_error variable. However, device A does not (immediately) check the async_error variable; it may continue to run its own suspend_noirq()/suspend_late() callback. This is bad.

We can resolve this problem by doing our error and wakeup checking (particularly, for the async_error flag) after waiting for children to suspend, instead of before. This also helps align the logic for the noirq and late suspend cases with the logic in __device_suspend().

It's easy to observe this erroneous behavior by, for example, forcing a device to sleep a bit in its suspend_noirq() (to ensure the parent is waiting for the child to complete), then return an error, and watch the parent suspend_noirq() still get called. (Or similarly, fake a wakeup event at the right (or is it wrong?) time.)

---
 drivers/base/power/main.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

@@ -1022,6 +1022,8 @@ static int __device_suspend_noirq(struct
 	TRACE_DEVICE(dev);
 	TRACE_SUSPEND(0);
 
+	dpm_wait_for_children(dev, async);
+
 	if (async_error)
 		goto Complete;
 

@@ -1033,8 +1035,6 @@ static int __device_suspend_noirq(struct
 	if (dev->power.syscore || dev->power.direct_complete)
 		goto Complete;
 
-	dpm_wait_for_children(dev, async);
-
 	if (dev->pm_domain) {
 		info = "noirq power domain ";
 		callback = pm_noirq_op(&dev->pm_domain->ops, state);

@@ -1169,6 +1169,8 @@ static int __device_suspend_late(struct
 
 	__pm_runtime_disable(dev, false);
 
+	dpm_wait_for_children(dev, async);
+
 	if (async_error)
 		goto Complete;
 

@@ -1180,8 +1182,6 @@ static int __device_suspend_late(struct
 	if (dev->power.syscore || dev->power.direct_complete)
 		goto Complete;
 
-	dpm_wait_for_children(dev, async);
-
 	if (dev->pm_domain) {
 		info = "late power domain ";
 		callback = pm_late_early_op(&dev->pm_domain->ops, state);

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

queue-4.4/pm-sleep-don-t-suspend-parent-when-async-child-suspend_-noirq-late-fails.patch