From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 755676B0005 for ; Mon, 6 Aug 2018 06:09:37 -0400 (EDT) Received: by mail-ed1-f70.google.com with SMTP id r21-v6so3834881edp.23 for ; Mon, 06 Aug 2018 03:09:37 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id 36-v6si6572100edn.295.2018.08.06.03.09.35 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 06 Aug 2018 03:09:35 -0700 (PDT) Date: Mon, 6 Aug 2018 12:09:28 +0200 From: Jan Kara Subject: Re: INFO: task hung in generic_file_write_iter Message-ID: <20180806100928.x7anab3c3y5q4ssa@quack2.suse.cz> References: <0000000000009ce88d05714242a8@google.com> <4b349bff-8ad4-6410-250d-593b13d8d496@I-love.SAKURA.ne.jp> <9b9fcdda-c347-53ee-fdbb-8a7d11cf430e@I-love.SAKURA.ne.jp> <20180720130602.f3d6dc4c943558875a36cb52@linux-foundation.org> 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: Tetsuo Handa Cc: Andrew Morton , Alexander Viro , syzbot , linux-mm@kvack.org, mgorman@techsingularity.net, Michal Hocko , ak@linux.intel.com, jack@suse.cz, jlayton@redhat.com, linux-kernel@vger.kernel.org, mawilcox@microsoft.com, syzkaller-bugs@googlegroups.com, tim.c.chen@linux.intel.com, linux-fsdevel On Tue 31-07-18 00:07:22, Tetsuo Handa wrote: > On 2018/07/21 5:06, Andrew Morton wrote: > > On Fri, 20 Jul 2018 19:36:23 +0900 Tetsuo Handa wrote: > > > >>> > >>> This report is stalling after mount() completed and process used remap_file_pages(). > >>> I think that we might need to use debug printk(). But I don't know what to examine. > >>> > >> > >> Andrew, can you pick up this debug printk() patch? > >> I guess we can get the result within one week. > > > > Sure, let's toss it in -next for a while. > > > >> >From 8f55e00b21fefffbc6abd9085ac503c52a302464 Mon Sep 17 00:00:00 2001 > >> From: Tetsuo Handa > >> Date: Fri, 20 Jul 2018 19:29:06 +0900 > >> Subject: [PATCH] fs/buffer.c: add debug print for __getblk_gfp() stall problem > >> > >> Among syzbot's unresolved hung task reports, 18 out of 65 reports contain > >> __getblk_gfp() line in the backtrace. Since there is a comment block that > >> says that __getblk_gfp() will lock up the machine if try_to_free_buffers() > >> attempt from grow_dev_page() is failing, let's start from checking whether > >> syzbot is hitting that case. This change will be removed after the bug is > >> fixed. > > > > I'm not sure that grow_dev_page() is hanging. It has often been > > suspected, but always is proven innocent. Lets see. > > syzbot reproduced this problem ( https://syzkaller.appspot.com/text?tag=CrashLog&x=11f2fc44400000 ) . > It says that grow_dev_page() is returning 1 but __find_get_block() is failing forever. Any idea? Looks like some kind of a race where device block size gets changed while getblk() runs (and creates buffers for underlying page). I don't have time to nail it down at this moment can have a look into it later unless someone beats me to it. Honza -- Jan Kara SUSE Labs, CR