3.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Lino Sanfilippo <LinoSanfilippo@xxxxxx> commit 03a1cec1f17ac1a6041996b3e40f96b5a2f90e1b upstream. Boyd Yang reported a problem for the case that multiple threads of the same thread group are waiting for a reponse for a permission event. In this case it is possible that some of the threads are never woken up, even if the response for the event has been received (see http://marc.info/?l=linux-kernel&m=131822913806350&w=2). The reason is that we are currently merging permission events if they belong to the same thread group. But we are not prepared to wake up more than one waiter for each event. We do wait_event(group->fanotify_data.access_waitq, event->response || atomic_read(&group->fanotify_data.bypass_perm)); and after that event->response = 0; which is the reason that even if we woke up all waiters for the same event some of them may see event->response being already set 0 again, then go back to sleep and block forever. With this patch we avoid that more than one thread is waiting for a response by not merging permission events for the same thread group any more. Reported-by: Boyd Yang <boyd.yang@xxxxxxxxx> Signed-off-by: Lino Sanfilippo <LinoSanfilipp@xxxxxx> Signed-off-by: Eric Paris <eparis@xxxxxxxxxx> Cc: Mihai Donțu <mihai.dontu@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/notify/fanotify/fanotify.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/fs/notify/fanotify/fanotify.c +++ b/fs/notify/fanotify/fanotify.c @@ -18,6 +18,12 @@ static bool should_merge(struct fsnotify old->tgid == new->tgid) { switch (old->data_type) { case (FSNOTIFY_EVENT_PATH): +#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS + /* dont merge two permission events */ + if ((old->mask & FAN_ALL_PERM_EVENTS) && + (new->mask & FAN_ALL_PERM_EVENTS)) + return false; +#endif if ((old->path.mnt == new->path.mnt) && (old->path.dentry == new->path.dentry)) return true; -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html