From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id F08796B0033 for ; Thu, 7 Dec 2017 12:08:11 -0500 (EST) Received: by mail-pf0-f198.google.com with SMTP id w7so6160662pfd.4 for ; Thu, 07 Dec 2017 09:08:11 -0800 (PST) Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id m8sor1166495plt.148.2017.12.07.09.08.10 for (Google Transport Security); Thu, 07 Dec 2017 09:08:10 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20171206050547.GA5260@X58A-UD3R> References: <94eb2c0d010a4e7897055f70535b@google.com> <20171204083339.GF8365@quack2.suse.cz> <80ba65b6-d0c2-2d3a-779b-a134af8a9054@lge.com> <20171206050547.GA5260@X58A-UD3R> From: Dmitry Vyukov Date: Thu, 7 Dec 2017 18:07:48 +0100 Message-ID: Subject: Re: possible deadlock in generic_file_write_iter (2) Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Byungchul Park 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 Wed, Dec 6, 2017 at 6:05 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. I've enabled CONFIG_BOOTPARAM_LOCKDEP_CROSSRELEASE_FULLSTACK. It should have the same effect, right? -- 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