Commit f283d227 authored Apr 01, 2012 by NeilBrown Committed by Jiri Kosina Apr 03, 2012

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>

parent b4a133da

drivers/char/apm-emulation.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -302,7 +302,7 @@ apm_ioctl(struct file *filp, u_int cmd, u_long arg)
		* anything critical, chill a bit on each iteration.
		*/
		while (wait_event_freezable(apm_suspend_waitqueue,
		as->suspend_state == SUSPEND_DONE))
		as->suspend_state != SUSPEND_ACKED))
		msleep(10);
		break;
		case SUSPEND_ACKTO: