linux-kernel - Re: WARNING: kobject bug in sysfs_warn

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Date:   Thu, 5 Apr 2018 10:19:50 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Greg KH <gregkh@...uxfoundation.org>, swhiteho@...hat.com,
        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

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.