From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C33F3C433E6 for ; Mon, 31 Aug 2020 10:03:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8939820693 for ; Mon, 31 Aug 2020 10:03:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726485AbgHaKDn (ORCPT ); Mon, 31 Aug 2020 06:03:43 -0400 Received: from mx2.suse.de ([195.135.220.15]:39574 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725964AbgHaKDm (ORCPT ); Mon, 31 Aug 2020 06:03:42 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id CA31EB702; Mon, 31 Aug 2020 10:04:15 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 7CA711E12CF; Mon, 31 Aug 2020 12:03:40 +0200 (CEST) Date: Mon, 31 Aug 2020 12:03:40 +0200 From: Jan Kara To: syzbot Cc: adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, tytso@mit.edu, linux-mm@kvack.org, Linus Torvalds , Oleg Nesterov Subject: Re: kernel BUG at fs/ext4/inode.c:LINE! Message-ID: <20200831100340.GA26519@quack2.suse.cz> References: <000000000000d3a33205add2f7b2@google.com> <20200828100755.GG7072@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200828100755.GG7072@quack2.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 28-08-20 12:07:55, Jan Kara wrote: > On Wed 26-08-20 19:48:16, syzbot wrote: > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: c3d8f220 Merge tag 'kbuild-fixes-v5.9' of git://git.kernel.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=15f83cb6900000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=bb68b9e8a8cc842f > > dashboard link: https://syzkaller.appspot.com/bug?extid=3622cea378100f45d59f > > compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81) > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1287ac96900000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11c7ac46900000 > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+3622cea378100f45d59f@syzkaller.appspotmail.com > > > > ------------[ cut here ]------------ > > kernel BUG at fs/ext4/inode.c:2598! > > invalid opcode: 0000 [#1] PREEMPT SMP KASAN > > CPU: 1 PID: 27612 Comm: syz-executor879 Not tainted 5.9.0-rc1-syzkaller #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > RIP: 0010:mpage_prepare_extent_to_map+0xd34/0xd40 fs/ext4/inode.c:2598 > > Doh, so this is: > > wait_on_page_writeback(page); > >>> BUG_ON(PageWriteback(page)); > > in mpage_prepare_extent_to_map(). So we have PageWriteback() page after we > have called wait_on_page_writeback() on a locked page. Not sure how this > could ever happen even less how ext4 could cause this... I was poking a bit into this and there were actually recent changes into page bit waiting logic by Linus. Linus, any idea? Honza -- Jan Kara SUSE Labs, CR