linux-kernel - [PATCH] PM: Prevent waiting forever on asynchronous resume after abort

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Date:	Wed,  1 Sep 2010 19:54:12 -0700
From:	Colin Cross <ccross@...roid.com>
To:	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org
Cc:	Colin Cross <ccross@...roid.com>, Pavel Machek <pavel@....cz>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Len Brown <len.brown@...el.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Alan Stern <stern@...land.harvard.edu>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] PM: Prevent waiting forever on asynchronous resume after abort

Only wait on a parent device during resume if the parent device is
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>
---
 drivers/base/power/main.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index cb784a0..e159910 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -526,7 +526,8 @@ static int device_resume(struct device *dev, pm_message_t state, bool async)
 	TRACE_DEVICE(dev);
 	TRACE_RESUME(0);
 
-	dpm_wait(dev->parent, async);
+	if (dev->parent && dev->parent->power.status >= DPM_OFF)
+		dpm_wait(dev->parent, async);
 	device_lock(dev);
 
 	dev->power.status = DPM_RESUMING;
-- 
1.7.1

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