From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f197.google.com (mail-wr0-f197.google.com [209.85.128.197]) by kanga.kvack.org (Postfix) with ESMTP id 9019D6B0253 for ; Fri, 27 Oct 2017 09:42:37 -0400 (EDT) Received: by mail-wr0-f197.google.com with SMTP id o44so3339970wrf.0 for ; Fri, 27 Oct 2017 06:42:37 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id x5si1312557wmf.159.2017.10.27.06.42.36 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 27 Oct 2017 06:42:36 -0700 (PDT) Date: Fri, 27 Oct 2017 15:42:34 +0200 From: Michal Hocko Subject: Re: possible deadlock in lru_add_drain_all Message-ID: <20171027134234.7dyx4oshjwd44vqx@dhcp22.suse.cz> References: <089e0825eec8955c1f055c83d476@google.com> <20171027093418.om5e566srz2ztsrk@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Dmitry Vyukov Cc: syzbot , Andrew Morton , Dan Williams , Johannes Weiner , Jan Kara , jglisse@redhat.com, LKML , linux-mm@kvack.org, shli@fb.com, syzkaller-bugs@googlegroups.com, Thomas Gleixner , Vlastimil Babka , ying.huang@intel.com On Fri 27-10-17 11:44:58, Dmitry Vyukov wrote: > On Fri, Oct 27, 2017 at 11:34 AM, Michal Hocko wrote: > > On Fri 27-10-17 02:22:40, syzbot wrote: > >> Hello, > >> > >> syzkaller hit the following crash on > >> a31cc455c512f3f1dd5f79cac8e29a7c8a617af8 > >> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master > >> compiler: gcc (GCC) 7.1.1 20170620 > >> .config is attached > >> Raw console output is attached. > > > > I do not see such a commit. My linux-next top is next-20171018 > > > > [...] > >> Chain exists of: > >> cpu_hotplug_lock.rw_sem --> &pipe->mutex/1 --> &sb->s_type->i_mutex_key#9 > >> > >> Possible unsafe locking scenario: > >> > >> CPU0 CPU1 > >> ---- ---- > >> lock(&sb->s_type->i_mutex_key#9); > >> lock(&pipe->mutex/1); > >> lock(&sb->s_type->i_mutex_key#9); > >> lock(cpu_hotplug_lock.rw_sem); > > > > I am quite confused about this report. Where exactly is the deadlock? > > I do not see where we would get pipe mutex from inside of the hotplug > > lock. Is it possible this is just a false possitive due to cross release > > feature? > > > As far as I understand this CPU0/CPU1 scheme works only for simple > cases with 2 mutexes. This seem to have larger cycle as denoted by > "the existing dependency chain (in reverse order) is:" section. My point was that lru_add_drain_all doesn't take any external locks other than lru_lock and that one is not anywhere in the chain AFAICS. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org