From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753231AbdLEJmC (ORCPT ); Tue, 5 Dec 2017 04:42:02 -0500 Received: from mx2.suse.de ([195.135.220.15]:39284 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753125AbdLEJly (ORCPT ); Tue, 5 Dec 2017 04:41:54 -0500 Date: Tue, 5 Dec 2017 10:41:50 +0100 From: Jan Kara To: Byungchul Park Cc: Jan Kara , syzbot , akpm@linux-foundation.org, hannes@cmpxchg.org, jlayton@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mgorman@techsingularity.net, npiggin@gmail.com, rgoldwyn@suse.com, syzkaller-bugs@googlegroups.com, peterz@infradead.org, kernel-team@lge.com Subject: Re: possible deadlock in generic_file_write_iter (2) Message-ID: <20171205094150.GA6076@quack2.suse.cz> References: <94eb2c0d010a4e7897055f70535b@google.com> <20171204083339.GF8365@quack2.suse.cz> <80ba65b6-d0c2-2d3a-779b-a134af8a9054@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <80ba65b6-d0c2-2d3a-779b-a134af8a9054@lge.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Byungchul, On Tue 05-12-17 13:58:09, Byungchul Park wrote: > On 12/4/2017 5:33 PM, Jan Kara wrote: > >adding Peter and Byungchul to CC since the lockdep report just looks > >strange and cross-release seems to be involved. Guys, how did #5 get into > >the lock chain and what does put_ucounts() have to do with sb_writers > >there? Thanks! > > Hello Jan, > > In order to get full stack of #5, we have to pass a boot param, > "crossrelease_fullstack", to the kernel. Now that it only informs > put_ucounts() in the call trace, it's hard to find out what exactly > happened at that time, but I can tell #5 shows: OK, thanks for the tip. > When acquire(sb_writers) in put_ucounts(), it was on the way to > complete((completion)&req.done) of wait_for_completion() in > devtmpfs_create_node(). > > If acquire(sb_writers) in put_ucounts() is stuck, then > wait_for_completion() in devtmpfs_create_node() would be also > stuck, since complete() being in the context of acquire(sb_writers) > cannot be called. But this is something I don't get: There aren't sb_writers anywhere near put_ucounts(). So why the heck did lockdep think that sb_writers are acquired by put_ucounts()? Honza -- Jan Kara SUSE Labs, CR