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APM: fix deadlock in APM_IOC_SUSPEND ioctl 

I found the Xorg server on my ARM device stuck in the 'msleep()' loop
in apm_ioctl.

I suspect it had attempted suspend immediately after resuming and lost
a race.
During that msleep(10);, a new suspend cycle must have started and
changed ->suspend_state to SUSPEND_PENDING, so it was never seen to
be SUSPEND_DONE and the loop could never exited.  It would have moved on
to SUSPEND_ACKTO but never been able to reach SUSPEND_DONE.

So change the loop to only run while SUSPEND_ACKED rather than until
SUSPEND_DONE.  This is much safer.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
This commit is contained in:
NeilBrown 2012-04-01 20:19:30 +10:00 committed by Jiri Kosina
parent b4a133da2e
commit f283d22713
1 changed files with 1 additions and 1 deletions
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2
drivers/char/apm-emulation.c
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@ -302,7 +302,7 @@ apm_ioctl(struct file *filp, u_int cmd, u_long arg)
* anything critical, chill a bit on each iteration. * anything critical, chill a bit on each iteration.
*/ */
while (wait_event_freezable(apm_suspend_waitqueue, while (wait_event_freezable(apm_suspend_waitqueue,
as->suspend_state == SUSPEND_DONE)) as->suspend_state != SUSPEND_ACKED))
msleep(10); msleep(10);
break; break;
case SUSPEND_ACKTO: case SUSPEND_ACKTO: