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SubjectSubject: [PATCH] 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>

diff --git a/drivers/char/apm-emulation.c b/drivers/char/apm-emulation.c
index f4837a8..6005c5c 100644
--- a/drivers/char/apm-emulation.c
+++ b/drivers/char/apm-emulation.c
@@ -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:[unhandled content-type:application/pgp-signature]
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