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Date:   Thu, 5 Apr 2018 09:36:19 +0100
From:   Steven Whitehouse <swhiteho@...hat.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>,
        Greg KH <gregkh@...uxfoundation.org>, rpeterso@...hat.com,
        cluster-devel@...hat.com
Cc:     syzbot <syzbot+ff87a28e665c163aa7f5@...kaller.appspotmail.com>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com
Subject: Re: WARNING: kobject bug in sysfs_warn_dup

Hi,


On 05/04/18 09:19, Dmitry Vyukov wrote:
> On Thu, Apr 5, 2018 at 8:34 AM, Greg KH <gregkh@...uxfoundation.org> 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@...kaller.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,

Steve.

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