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authorLino Sanfilippo <LinoSanfilippo@gmx.de>2012-03-23 02:42:23 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-10-01 09:10:52 -0700
commitdb68549fe3aee4045e1d7348b20d7c8baf4518c0 (patch)
tree9169045efdd981f5042ad103fbe3e816edce2892
parent1d48ca6f38fa39298474708abebeffef4ef2cd2d (diff)
downloadlinux-linaro-stable-db68549fe3aee4045e1d7348b20d7c8baf4518c0.tar.gz
fanotify: dont merge permission events
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@gmail.com> Signed-off-by: Lino Sanfilippo <LinoSanfilipp@gmx.de> Signed-off-by: Eric Paris <eparis@redhat.com> Cc: Mihai Donțu <mihai.dontu@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--fs/notify/fanotify/fanotify.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index a50636025364..0c2f9122b262 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -18,6 +18,12 @@ static bool should_merge(struct fsnotify_event *old, struct fsnotify_event *new)
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;