From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751322AbaAMGEq (ORCPT ); Mon, 13 Jan 2014 01:04:46 -0500 Received: from cantor2.suse.de ([195.135.220.15]:52995 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751220AbaAMGEo (ORCPT ); Mon, 13 Jan 2014 01:04:44 -0500 Date: Mon, 13 Jan 2014 07:04:41 +0100 From: Jan Kara To: Hugh Dickins Cc: Jan Kara , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [PATCH mmotm/next] fanotify: fix corruption preventing startup Message-ID: <20140113060441.GB3837@quack.suse.cz> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat 11-01-14 22:54:15, Hugh Dickins wrote: > Two of my machines couldn't boot mmotm with fanotify enabled: > 0x40000020 was being or'ed into a group's notification_waitq next > pointer, with sad results. It comes from an over-simplification in > fanotify_merge(): test_event isn't NULL when the loop finds no merge. That's a really dumb bug. Thanks for the fix! It looks good, you can add: Reviewed-by: Jan Kara I was wondering why I didn't see this problem during my testing. I was always running my tests with various debug options enabled (in a hope to catch more problems ;), in particular with spinlock debugging enabled which shifted the waitqueue pointers further and the corruption landed in spinlock debugging fields and never got noticed... Ew :-| Honza > > Signed-off-by: Hugh Dickins > --- > Fixes fsnotify-do-not-share-events-between-notification-groups.patch > > fs/notify/fanotify/fanotify.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > --- mmotm/fs/notify/fanotify/fanotify.c 2014-01-10 18:25:01.700448941 -0800 > +++ linux/fs/notify/fanotify/fanotify.c 2014-01-11 22:15:31.580961010 -0800 > @@ -37,16 +37,19 @@ static bool should_merge(struct fsnotify > static struct fsnotify_event *fanotify_merge(struct list_head *list, > struct fsnotify_event *event) > { > - struct fsnotify_event *test_event = NULL; > + struct fsnotify_event *test_event; > + bool do_merge = false; > > pr_debug("%s: list=%p event=%p\n", __func__, list, event); > > list_for_each_entry_reverse(test_event, list, list) { > - if (should_merge(test_event, event)) > + if (should_merge(test_event, event)) { > + do_merge = true; > break; > + } > } > > - if (!test_event) > + if (!do_merge) > return NULL; > > test_event->mask |= event->mask; -- Jan Kara SUSE Labs, CR