Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753550AbdHQU46 (ORCPT ); Thu, 17 Aug 2017 16:56:58 -0400 Received: from mail.kernel.org ([198.145.29.99]:45830 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753449AbdHQU44 (ORCPT ); Thu, 17 Aug 2017 16:56:56 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 84B7622B5F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=rostedt@goodmis.org Date: Thu, 17 Aug 2017 16:56:52 -0400 From: Steven Rostedt To: Bart Van Assche Cc: "longman@redhat.com" , "bfields@fieldses.org" , "mingo@kernel.org" , "jlayton@poochiereds.net" , "linux-block@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "axboe@kernel.dk" , "linux-fsdevel@vger.kernel.org" Subject: Re: [PATCH v2] blktrace: Fix potentail deadlock between delete & sysfs ops Message-ID: <20170817165652.5eeca878@gandalf.local.home> In-Reply-To: <1503002469.2615.13.camel@wdc.com> References: <1502916040-18067-1-git-send-email-longman@redhat.com> <20170817093444.3276f7ab@gandalf.local.home> <20170817163056.19ea42c8@gandalf.local.home> <1503002469.2615.13.camel@wdc.com> X-Mailer: Claws Mail 3.14.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2216 Lines: 48 On Thu, 17 Aug 2017 20:41:10 +0000 Bart Van Assche wrote: > On Thu, 2017-08-17 at 16:30 -0400, Steven Rostedt wrote: > > On Thu, 17 Aug 2017 12:24:39 -0400 > > Waiman Long wrote: > > > > > On 08/17/2017 09:34 AM, Steven Rostedt wrote: > > > > On Wed, 16 Aug 2017 16:40:40 -0400 > > > > Waiman Long wrote: > > > > > > > > > The lockdep code had reported the following unsafe locking scenario: > > > > > > > > > > CPU0 CPU1 > > > > > ---- ---- > > > > > lock(s_active#228); > > > > > lock(&bdev->bd_mutex/1); > > > > > lock(s_active#228); > > > > > lock(&bdev->bd_mutex); > > > > > > > > Can you show the exact locations of these locks. I have no idea where > > > > this "s_active" is. > > > > > > The s_active isn't an actual lock. It is a reference count (kn->count) > > > on the sysfs (kernfs) file. Removal of a sysfs file, however, require > > > a wait until all the references are gone. The reference count is > > > treated like a rwsem using lockdep instrumentation code. > > > > Which kernel is this? I don't see any lockdep annotation around > > kn->count (doing a git grep, I find it referenced in fs/kernfs/dir.c) > > As far as I know the s_active lockdep annotations were introduced in 2007 > through commit 0ab66088c855 ("sysfs: implement sysfs_dirent active reference > and immediate disconnect"). Today these annotations exist in kernfs: > $ git grep -nHw dep_map fs/kernfs > fs/kernfs/dir.c:421: rwsem_acquire_read(&kn->dep_map, 0, 1, _RET_IP_); > fs/kernfs/dir.c:441: rwsem_release(&kn->dep_map, 1, _RET_IP_); > fs/kernfs/dir.c:468: rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_); > fs/kernfs/dir.c:470: lock_contended(&kn->dep_map, _RET_IP_); > fs/kernfs/dir.c:478: lock_acquired(&kn->dep_map, _RET_IP_); > fs/kernfs/dir.c:479: rwsem_release(&kn->dep_map, 1, _RET_IP_); > fs/kernfs/dir.c:1385: rwsem_acquire(&kn->dep_map, 0, 1, _RET_IP_); > fs/kernfs/file.c:1000: lockdep_init_map(&kn->dep_map, "s_active", key, 0); > Ah thanks. I was searching for the wrong thing. :-/ -- Steve