[PATCH 3/6] fsnotify: Drop notification_mutex before destroying event

[Jan Kara <jack@suse.cz>]

fsnotify_flush_notify() and fanotify_release() destroy notification
event while holding notification_mutex. Destruction of fanotify event
includes a path_put() call which may end up calling into a filesystem to
delete an inode if we happen to be the last holders of dentry reference
which happens to be the last holder of inode reference. That may violate
lock ordering for some filesystems since notification_mutex is also
acquired e. g. during write when generating fanotify event. Also this is
the only thing that forces notification_mutex to be a sleeping lock.  So
drop notification_mutex before destroying a notification event.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/notify/fanotify/fanotify_user.c | 6 ++++--
 fs/notify/notification.c           | 2 ++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index a64313868d3a..46d135c4988f 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -390,9 +390,11 @@ static int fanotify_release(struct inode *ignored, struct file *file)
 	mutex_lock(&group->notification_mutex);
 	while (!fsnotify_notify_queue_is_empty(group)) {
 		fsn_event = fsnotify_remove_first_event(group);
-		if (!(fsn_event->mask & FAN_ALL_PERM_EVENTS))
+		if (!(fsn_event->mask & FAN_ALL_PERM_EVENTS)) {
+			mutex_unlock(&group->notification_mutex);
 			fsnotify_destroy_event(group, fsn_event);
-		else
+			mutex_lock(&group->notification_mutex);
+		} else
 			FANOTIFY_PE(fsn_event)->response = FAN_ALLOW;
 	}
 	mutex_unlock(&group->notification_mutex);
diff --git a/fs/notify/notification.c b/fs/notify/notification.c
index e455e83ceeeb..7d563dea52a4 100644
--- a/fs/notify/notification.c
+++ b/fs/notify/notification.c
@@ -178,7 +178,9 @@ void fsnotify_flush_notify(struct fsnotify_group *group)
 	mutex_lock(&group->notification_mutex);
 	while (!fsnotify_notify_queue_is_empty(group)) {
 		event = fsnotify_remove_first_event(group);
+		mutex_unlock(&group->notification_mutex);
 		fsnotify_destroy_event(group, event);
+		mutex_lock(&group->notification_mutex);
 	}
 	mutex_unlock(&group->notification_mutex);
 }
-- 
2.6.6