From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:43343 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760349AbcIMUPo (ORCPT ); Tue, 13 Sep 2016 16:15:44 -0400 From: Jan Kara To: Andrew Morton Cc: linux-fsdevel@vger.kernel.org, Miklos Szeredi , Lino Sanfilippo , Eric Paris , Al Viro , Jan Kara Subject: [PATCH 6/6] fanotify: Fix possible false warning when freeing events Date: Tue, 13 Sep 2016 22:15:11 +0200 Message-Id: <1473797711-14111-7-git-send-email-jack@suse.cz> In-Reply-To: <1473797711-14111-1-git-send-email-jack@suse.cz> References: <1473797711-14111-1-git-send-email-jack@suse.cz> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: When freeing permission events by fsnotify_destroy_event(), the warning WARN_ON(!list_empty(&event->list)); may falsely hit. This is because although fanotify_get_response() saw event->response set, there is nothing to make sure the current CPU also sees the removal of the event from the list. Add proper locking around the WARN_ON() to avoid the false warning. Reported-by: Miklos Szeredi Signed-off-by: Jan Kara --- fs/notify/notification.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/fs/notify/notification.c b/fs/notify/notification.c index 070d255b24a2..6b7f430bb2de 100644 --- a/fs/notify/notification.c +++ b/fs/notify/notification.c @@ -73,8 +73,17 @@ void fsnotify_destroy_event(struct fsnotify_group *group, /* Overflow events are per-group and we don't want to free them */ if (!event || event->mask == FS_Q_OVERFLOW) return; - /* If the event is still queued, we have a problem... */ - WARN_ON(!list_empty(&event->list)); + /* + * If the event is still queued, we have a problem... Do an unreliable + * lockless check first to avoid locking in the common case. The + * locking may be necessary for permission events which got removed + * from the list by a different CPU than the one freeing the event. + */ + if (!list_empty(&event->list)) { + spin_lock(&group->notification_lock); + WARN_ON(!list_empty(&event->list)); + spin_unlock(&group->notification_lock); + } group->ops->free_event(event); } -- 2.6.6