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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 DFF69C282CE for ; Wed, 10 Apr 2019 00:26:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B87AB20850 for ; Wed, 10 Apr 2019 00:26:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726926AbfDJA0L (ORCPT ); Tue, 9 Apr 2019 20:26:11 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:55920 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726592AbfDJA0K (ORCPT ); Tue, 9 Apr 2019 20:26:10 -0400 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92 #3 (Red Hat Linux)) id 1hE13z-0002Nr-KK; Wed, 10 Apr 2019 00:26:03 +0000 Date: Wed, 10 Apr 2019 01:26:03 +0100 From: Al Viro To: syzbot Cc: akpm@linux-foundation.org, amir73il@gmail.com, dvyukov@google.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, penguin-kernel@i-love.sakura.ne.jp, raven@themaw.net, syzkaller-bugs@googlegroups.com Subject: Re: kernel BUG at fs/inode.c:LINE! Message-ID: <20190410002603.GS2217@ZenIV.linux.org.uk> References: <00000000000051e9c2057d31a563@google.com> <00000000000036a4a9058619dff3@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <00000000000036a4a9058619dff3@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Apr 09, 2019 at 07:36:00AM -0700, syzbot wrote: > Bisection is inconclusive: the first bad commit could be any of: [snip the useless pile] > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=15e1fc2b200000 > start commit: [unknown > git tree: linux-next > dashboard link: https://syzkaller.appspot.com/bug?extid=5399ed0832693e29f392 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=101032b3400000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16534063400000 > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection If I'm not misreading the "crash report" there, it has injected an allocation failure in dentry allocation in d_make_root() from autofs_fill_super() ( root_inode = autofs_get_inode(s, S_IFDIR | 0755); root = d_make_root(root_inode); ) which has triggered iput() on the inode passed to d_make_root() (as it ought to). At which point it stepped into some BUG_ON() in fs/inode.c, but I've no idea which one it is - line numbers do not match anything in linux-next or in mainline. Reported line 1566 is if (inode->i_nlink && (inode->i_state & I_DIRTY_TIME)) { in all of them; as the matter of fact, the diff in fs/inode.c between -next and mainline is empty. There is a BUG_ON() several lines prior, and in 4.20 it used to be line 1566, so _probably_ that's what it is. With that assumption, it's BUG_ON(inode->i_state & I_CLEAR); IOW, we'd got I_CLEAR in the inode passed to d_make_root() there. Which should not happen - the inode must have come from new_inode(), which gets it from new_inode_pseudo(), which zeroes ->i_state. And I_CLEAR is set only in clear_inode(). For autofs inodes that can come only from autofs_evict_inode(), called as ->evict() from evict_inode(). Which should never ever be called for inode with positive ->i_count... It might be memory corruption; it might be a dangling inode pointer somewhere, it might be something else. To get any further we really need a confirmation of the identity of triggered BUG_ON(). As an aside, your "sample crash reports" would've been much more useful if they went with commit SHA1 in question, especially when they contain line numbers.