From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f199.google.com (mail-io0-f199.google.com [209.85.223.199]) by kanga.kvack.org (Postfix) with ESMTP id 6D6196B0253 for ; Fri, 27 Oct 2017 05:45:20 -0400 (EDT) Received: by mail-io0-f199.google.com with SMTP id 189so10881720iow.8 for ; Fri, 27 Oct 2017 02:45:20 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id d202sor3301790iod.345.2017.10.27.02.45.19 for (Google Transport Security); Fri, 27 Oct 2017 02:45:19 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20171027093418.om5e566srz2ztsrk@dhcp22.suse.cz> References: <089e0825eec8955c1f055c83d476@google.com> <20171027093418.om5e566srz2ztsrk@dhcp22.suse.cz> From: Dmitry Vyukov Date: Fri, 27 Oct 2017 11:44:58 +0200 Message-ID: Subject: Re: possible deadlock in lru_add_drain_all Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko 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, 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. -- 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