MD: Add del_timer_sync to mddev_suspend (fix nasty panic)

Use del_timer_sync to remove timer before mddev_suspend finishes.

We don't want a timer going off after an mddev_suspend is called.  This is
especially true with device-mapper, since it can call the destructor function
immediately following a suspend.  This results in the removal (kfree) of the
structures upon which the timer depends - resulting in a very ugly panic.
Therefore, we add a del_timer_sync to mddev_suspend to prevent this.

Cc: [email protected]
Signed-off-by: NeilBrown <[email protected]>

drivers/md/md.c

@@ -391,6 +391,8 @@ void mddev_suspend(struct mddev *mddev)
 	synchronize_rcu();
 	wait_event(mddev->sb_wait, atomic_read(&mddev->active_io) == 0);
 	mddev->pers->quiesce(mddev, 1);
+
+	del_timer_sync(&mddev->safemode_timer);
 }
 EXPORT_SYMBOL_GPL(mddev_suspend);