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[209.132.180.67]) by mx.google.com with ESMTP id d12si825067pgn.704.2018.04.11.08.12.03; Wed, 11 Apr 2018 08:12:42 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=D46+ygjn; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753383AbeDKPFR (ORCPT + 99 others); Wed, 11 Apr 2018 11:05:17 -0400 Received: from mail-pf0-f178.google.com ([209.85.192.178]:34136 "EHLO mail-pf0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752894AbeDKPFP (ORCPT ); Wed, 11 Apr 2018 11:05:15 -0400 Received: by mail-pf0-f178.google.com with SMTP id q9so1085617pff.1 for ; Wed, 11 Apr 2018 08:05:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=Fx+p6Yu/9pIKP+dDFUa9nEIDuQR8N+Uf36lW7aU6yWg=; b=D46+ygjnTPQgJPkJn+GXeS6QVH1/hl4p4rwlEJ+Ir2lfu5LZlxkAF33AHq6/P6TttT p6ChoUAr/aF5H3ifGSYmQrFfDJtCsd7ov6KYQZxR7hIn3L41nVQc0Me7ZhwzpVRbpT82 omgtqOpdvFl3nR7vDlsS+Lc6SgzZb8pWcGyVvz7LXaXvrQFAKW3+N7HTmgKjEbKg1Unx pYfidC/BE/isnwJmoJ7xZ+ZXiM10JRZIn9UvyDZTpEovZFwUqFeWLoH7nF2yjNoozDRR ZakijyLiZX+qMUK5uYIpllN2pjZUkmzf1Px03WJfoJNIDGSbiNWmcsRUIpqEMLquNp4W DuJA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=Fx+p6Yu/9pIKP+dDFUa9nEIDuQR8N+Uf36lW7aU6yWg=; b=NzWAUbIJYfsnFXLvOyu3kBpHAI7WVWfbtKq6JffQnsk9xZcZgNZ92kybawpwMBG03f FmB7snlQeMq1iBvS7AC9allaFKOimVLaGzz7x9hI8JmRKqobvfWpnJzVGRzDZqiugpxP NyDHZeeSFrNRBsqR60XvRP9LR41MaGD22SNvg/e16bYr4rONMKM5dItx62Ln2H+Ete88 I1ZdsiaNIsOBxoCBqj7LB41/OSDif7tockoG3pEB2mU12o74CU8Zn7A7XZOh+XjfymP+ Gs/F+uF4Gxkzp04alBe1A6oqR9VOIWnJLXY83JtKy2xC+ek8MqGSr2rFr8bmHBq8jrhC o2ew== X-Gm-Message-State: ALQs6tBGviILJGiYdiagUuSBFR4MpMWrEaY5ydyOJxPgFzhWqIDgiL0a u4nJGV7ElgTsiUOIUE/enqoS8iJNborp1zuFQnt8Cw== X-Received: by 10.101.64.7 with SMTP id f7mr3825078pgp.216.1523459115076; Wed, 11 Apr 2018 08:05:15 -0700 (PDT) MIME-Version: 1.0 Received: by 10.100.182.136 with HTTP; Wed, 11 Apr 2018 08:04:54 -0700 (PDT) In-Reply-To: <20180405142344.GC29178@kroah.com> References: <20180405063444.GA5877@kroah.com> <26e497b0-1e10-d9c6-73eb-e0feed9a60ea@redhat.com> <97ada9f8-93e0-b321-e588-2d3b34b10ef8@redhat.com> <20180405133430.GA21390@kroah.com> <20180405142344.GC29178@kroah.com> From: Dmitry Vyukov Date: Wed, 11 Apr 2018 17:04:54 +0200 Message-ID: Subject: Re: WARNING: kobject bug in sysfs_warn_dup To: Greg KH Cc: Steven Whitehouse , rpeterso@redhat.com, cluster-devel@redhat.com, syzbot , LKML , syzkaller-bugs Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 5, 2018 at 4:23 PM, Greg KH wrote: >> >> On 05/04/18 09:52, Dmitry Vyukov wrote: >> >> > On Thu, Apr 5, 2018 at 10:36 AM, Steven Whitehouse wrote: >> >> > > Hi, >> >> > > >> >> > > >> >> > > >> >> > > On 05/04/18 09:19, Dmitry Vyukov wrote: >> >> > > > On Thu, Apr 5, 2018 at 8:34 AM, Greg KH >> >> > > > wrote: >> >> > > > > On Wed, Apr 04, 2018 at 07:02:01PM -0700, syzbot wrote: >> >> > > > > > Hello, >> >> > > > > > >> >> > > > > > syzbot hit the following crash on upstream commit >> >> > > > > > 3e968c9f1401088abc9a19ae6ff571644d37a355 (Wed Apr 4 21:19:24 2018 +0000) >> >> > > > > > Merge tag 'ext4_for_linus' of >> >> > > > > > git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4 >> >> > > > > > syzbot dashboard link: >> >> > > > > > https://syzkaller.appspot.com/bug?extid=ff87a28e665c163aa7f5 >> >> > > > > > >> >> > > > > > C reproducer: >> >> > > > > > https://syzkaller.appspot.com/x/repro.c?id=5104666266304512 >> >> > > > > > syzkaller reproducer: >> >> > > > > > https://syzkaller.appspot.com/x/repro.syz?id=5683447737614336 >> >> > > > > > Raw console output: >> >> > > > > > https://syzkaller.appspot.com/x/log.txt?id=5104818200772608 >> >> > > > > > Kernel config: >> >> > > > > > https://syzkaller.appspot.com/x/.config?id=9118669095563550941 >> >> > > > > > compiler: gcc (GCC) 7.1.1 20170620 >> >> > > > > > >> >> > > > > > IMPORTANT: if you fix the bug, please add the following tag to the >> >> > > > > > commit: >> >> > > > > > Reported-by: syzbot+ff87a28e665c163aa7f5@syzkaller.appspotmail.com >> >> > > > > > It will help syzbot understand when the bug is fixed. See footer for >> >> > > > > > details. >> >> > > > > > If you forward the report, please keep this part and the footer. >> >> > > > > > >> >> > > > > > R10: 0000000000000000 R11: 0000000000000286 R12: 0000000000000003 >> >> > > > > > R13: 0000000000000004 R14: 0000000000000000 R15: 0000000000000000 >> >> > > > > > ------------[ cut here ]------------ >> >> > > > > > kobject_add_internal failed for nodev( with -EEXIST, don't try to >> >> > > > > > register >> >> > > > > > things with the same name in the same directory. >> >> > > > > > sysfs: cannot create duplicate filename '/fs/gfs2/nodev(' >> >> > > > > > WARNING: CPU: 1 PID: 4473 at lib/kobject.c:238 >> >> > > > > > kobject_add_internal+0x8d4/0xbc0 lib/kobject.c:235 >> >> > > > > > CPU: 0 PID: 4474 Comm: syzkaller533472 Not tainted 4.16.0+ #15 >> >> > > > > > Kernel panic - not syncing: panic_on_warn set ... >> >> > > > > > >> >> > > > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS >> >> > > > > > Google 01/01/2011 >> >> > > > > > Call Trace: >> >> > > > > > __dump_stack lib/dump_stack.c:17 [inline] >> >> > > > > > dump_stack+0x1a7/0x27d lib/dump_stack.c:53 >> >> > > > > > sysfs_warn_dup+0x83/0xa0 fs/sysfs/dir.c:30 >> >> > > > > > sysfs_create_dir_ns+0x178/0x1d0 fs/sysfs/dir.c:58 >> >> > > > > > create_dir lib/kobject.c:69 [inline] >> >> > > > > > kobject_add_internal+0x335/0xbc0 lib/kobject.c:227 >> >> > > > > > kobject_add_varg lib/kobject.c:364 [inline] >> >> > > > > > kobject_init_and_add+0xf9/0x150 lib/kobject.c:436 >> >> > > > > > gfs2_sys_fs_add+0x1ff/0x580 fs/gfs2/sys.c:652 >> >> > > > > > fill_super+0x86f/0x1d70 fs/gfs2/ops_fstype.c:1118 >> >> > > > > > gfs2_mount+0x587/0x6e0 fs/gfs2/ops_fstype.c:1321 >> >> > > > > gfs2 bug, not a sysfs bug, we are correctly warning about an incorrect >> >> > > > > usage of the api. >> >> > > > Then +gfs2 maintainers. >> >> > > > >> >> > > > > Now if we should turn this into a non-WARN message, that's a different >> >> > > > > thing, I'll gladly take a patch for that. >> >> > > > If it's API usage bug in higher level code, then I think WARN is a >> >> > > > proper thing. We already had similar ones and they were fixed. >> >> > > >> >> > > I'm trying to figure out what the test is doing, but it is not very clear. >> >> > > At a guess I'd say that perhaps it is trying to mount multiple filesystems >> >> > > with the same label? If that is the case then it is not allowed, and it >> >> > > should be caught be the sysfs code and result in a refusal to mount, which >> >> > > is what I think I see here. Knowing which sysfs directory is involved would >> >> > > allow us to confirm, but I suspect that the test needs altering to give each >> >> > > gfs2 mount a different label at an initial guess, >> >> > >> >> > Hi Steve, >> >> > >> >> > But Greg claims that this is incorrect usage of sysfs API: >> >> > >> >> > > gfs2 bug, not a sysfs bug, we are correctly warning about an incorrect >> >> > > usage of the api. >> >> > I think this means that sysfs callers must not try to create the same >> >> > thing twice. >> >> > >> >> > Either way user-space code must not be able to triggers WARNINGs in >> >> > kernel. If it does than this is something to fix in kernel. >> >> >> >> I guess that this warning was added more recently as I've not seen it >> >> before. >> > >> > No, it has been there since at least the 3.13 kernel release (back in >> > 2013), which is where it got moved to a separate function, but the logic >> > has been around in the kernel tree for much longer than that as seen in >> > commit d1c1459e4594 ("sysfs: separate out dup filename warning into a >> > separate function") >> > >> >> My expectation is that it will return -EEXIST and not print a >> >> warning there. To avoid that we would have to create a new list of GFS2 >> >> superblocks, and check the list for each mount I think. We could do that, >> >> but it seems a bit odd to duplicate code that is already there and working. >> > >> > Don't you have a list of the "names" of the things you are creating >> > somewhere? Or are you relying on sysfs to do your housekeeping for you? >> > >> > Also, why did this trigger a syzbot report? It's only a dump_stack() >> > reference, one showing that yes, this is something that should not be >> > done, but the kernel keeps on working afterward. >> >> There is a WARN(), not just dump_stack(): >> >> WARN(1, "%s failed for %s with " >> "-EEXIST, don't try to register things with " >> "the same name in the same directory.\n", >> __func__, kobject_name(kobj)); > > Ah, that's a kobject warning, not a sysfs one. Was looking too far down > the call chain. We can change this to be dump_stack() as well if you > think that would help out. Maybe remove it entirely as sysfs already > does dump the stack? kobject_add is called not only from sysfs, right? I was just going to send a patch that changes WARN to pr_err+dump_stack, but noticed that we have 4 active bugs on this WARNING: WARNING: kobject bug in gfs2_sys_fs_add https://syzkaller.appspot.com/bug?id=057673a56dab61b3a447989b67f10b205111c8f4 WARNING: kobject bug in br_add_if https://syzkaller.appspot.com/bug?id=3e0339080acd6a2a350a900bc6533b03f5498490 WARNING: kobject bug in netdev_queue_update_kobjects https://syzkaller.appspot.com/bug?id=86a8e2ab50527d5a5eb4fad2fc15df609f22d86a WARNING: kobject bug in device_add https://syzkaller.appspot.com/bug?id=57eba87aff7669512fb68e56a932b01805342d13 We want to ignore all of them? As a side signal none of them got any attention, except Eric noting that, yes, it is noisy: https://groups.google.com/d/msg/syzkaller-bugs/XDTC7Iv4IKY/Ab_tgZ4HAQAJ So I guess I will still mail the patch.