From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f72.google.com (mail-pg0-f72.google.com [74.125.83.72]) by kanga.kvack.org (Postfix) with ESMTP id 6FD276B033F for ; Wed, 6 Dec 2017 00:06:10 -0500 (EST) Received: by mail-pg0-f72.google.com with SMTP id d4so1905106pgv.4 for ; Tue, 05 Dec 2017 21:06:10 -0800 (PST) Received: from lgeamrelo12.lge.com (LGEAMRELO12.lge.com. [156.147.23.52]) by mx.google.com with ESMTP id q3si1376236pfl.322.2017.12.05.21.06.08 for ; Tue, 05 Dec 2017 21:06:09 -0800 (PST) Date: Wed, 6 Dec 2017 14:05:47 +0900 From: Byungchul Park Subject: Re: possible deadlock in generic_file_write_iter (2) Message-ID: <20171206050547.GA5260@X58A-UD3R> 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: Sender: owner-linux-mm@kvack.org List-ID: To: Dmitry Vyukov Cc: Jan Kara , syzbot , Andrew Morton , Johannes Weiner , jlayton@redhat.com, LKML , Linux-MM , Mel Gorman , npiggin@gmail.com, rgoldwyn@suse.com, syzkaller-bugs@googlegroups.com, Peter Zijlstra , kernel-team@lge.com On Tue, Dec 05, 2017 at 10:19:07AM +0100, Dmitry Vyukov wrote: > On Tue, Dec 5, 2017 at 5:58 AM, Byungchul Park wrote: > > 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. > > Hi, > > What is cross-release? Is it something new? Should we always enable > crossrelease_fullstack during testing? Hello Dmitry, Yes, it's new one making lockdep track wait_for_completion() as well. And we should enable crossrelease_fullstack if you don't care system slowdown but testing. -- Thanks, Byungchul -- 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