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>

diff --git a/drivers/char/apm-emulation.c b/drivers/char/apm-emulation.c
index f4837a8..6005c5c 100644 (file)
--- 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: