linux-kernel - [67/80] PM: Prevent waiting forever on asynchronous resume after failing suspend

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Date:	Fri, 24 Sep 2010 09:24:55 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Colin Cross <ccross@...roid.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: [67/80] PM: Prevent waiting forever on asynchronous resume after failing suspend

2.6.35-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Colin Cross <ccross@...roid.com>

commit 152e1d592071c8b312bb898bc1118b64e4aea535 upstream.

During suspend, the power.completion is expected to be set when a
device has not yet started suspending.  Set it on init to fix a
corner case where a device is resumed when its parent has never
suspended.

Consider three drivers, A, B, and C.  The parent of A is C, and C
has async_suspend set.  On boot, C->power.completion is initialized
to 0.

During the first suspend:
suspend_devices_and_enter(...)
 dpm_resume(...)
  device_suspend(A)
  device_suspend(B) returns error, aborts suspend
 dpm_resume_end(...)
   dpm_resume(...)
    device_resume(A)
     dpm_wait(A->parent == C)
      wait_for_completion(C->power.completion)

The wait_for_completion will never complete, because
complete_all(C->power.completion) will only be called from
device_suspend(C) or device_resume(C), neither of which is called
if suspend is aborted before C.

After a successful suspend->resume cycle, where B doesn't abort
suspend, C->power.completion is left in the completed state by the
call to device_resume(C), and the same call path will work if B
aborts suspend.

Signed-off-by: Colin Cross <ccross@...roid.com>
Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/base/power/main.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -59,6 +59,7 @@ void device_pm_init(struct device *dev)
 {
 	dev->power.status = DPM_ON;
 	init_completion(&dev->power.completion);
+	complete_all(&dev->power.completion);
 	pm_runtime_init(dev);
 }

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