From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752457AbdLEE6M (ORCPT ); Mon, 4 Dec 2017 23:58:12 -0500 Received: from LGEAMRELO13.lge.com ([156.147.23.53]:44708 "EHLO lgeamrelo13.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752065AbdLEE6L (ORCPT ); Mon, 4 Dec 2017 23:58:11 -0500 X-Original-SENDERIP: 156.147.1.126 X-Original-MAILFROM: byungchul.park@lge.com X-Original-SENDERIP: 10.177.222.184 X-Original-MAILFROM: byungchul.park@lge.com Subject: Re: possible deadlock in generic_file_write_iter (2) To: Jan Kara , syzbot Cc: 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 References: <94eb2c0d010a4e7897055f70535b@google.com> <20171204083339.GF8365@quack2.suse.cz> From: Byungchul Park Message-ID: <80ba65b6-d0c2-2d3a-779b-a134af8a9054@lge.com> Date: Tue, 5 Dec 2017 13:58:09 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <20171204083339.GF8365@quack2.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/4/2017 5:33 PM, Jan Kara wrote: > Hello, > > 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: 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. This is why cross-release added the lock chain. -- Thanks, Byungchul