[Cluster-devel] WARNING: kobject bug in sysfs_warn_dup

[Cluster-devel] WARNING: kobject bug in sysfs_warn_dup

[Dmitry Vyukov]

On Thu, Apr 5, 2018 at 8:34 AM, Greg KH <gregkh@linuxfoundation.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 at 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.

[Cluster-devel] WARNING: kobject bug in sysfs_warn_dup

[Steven Whitehouse]

Hi,


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

Steve.

[Cluster-devel] WARNING: kobject bug in sysfs_warn_dup

[Dmitry Vyukov]

On Thu, Apr 5, 2018 at 10:36 AM, Steven Whitehouse <swhiteho@redhat.com> wrote:
> Hi,
>
>
>
> On 05/04/18 09:19, Dmitry Vyukov wrote:
>>
>> On Thu, Apr 5, 2018 at 8:34 AM, Greg KH <gregkh@linuxfoundation.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 at 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.

[Cluster-devel] WARNING: kobject bug in sysfs_warn_dup

[Steven Whitehouse]

Hi,


On 05/04/18 09:52, Dmitry Vyukov wrote:
> On Thu, Apr 5, 2018 at 10:36 AM, Steven Whitehouse <swhiteho@redhat.com> wrote:
>> Hi,
>>
>>
>>
>> On 05/04/18 09:19, Dmitry Vyukov wrote:
>>> On Thu, Apr 5, 2018 at 8:34 AM, Greg KH <gregkh@linuxfoundation.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 at 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. 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.

So it sounds like a case of differing assumptions about what is a valid 
use of the sysfs api. Shouldn't be too hard to fix though,

Steve.

[Cluster-devel] WARNING: kobject bug in sysfs_warn_dup

[Dmitry Vyukov]

On Thu, Apr 5, 2018 at 11:00 AM, Steven Whitehouse <swhiteho@redhat.com> wrote:
> Hi,
>
>
>
> On 05/04/18 09:52, Dmitry Vyukov wrote:
>>
>> On Thu, Apr 5, 2018 at 10:36 AM, Steven Whitehouse <swhiteho@redhat.com>
>> wrote:
>>>
>>> Hi,
>>>
>>>
>>>
>>> On 05/04/18 09:19, Dmitry Vyukov wrote:
>>>>
>>>> On Thu, Apr 5, 2018 at 8:34 AM, Greg KH <gregkh@linuxfoundation.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 at 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. 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.
>
> So it sounds like a case of differing assumptions about what is a valid use
> of the sysfs api. Shouldn't be too hard to fix though,


Greg?

Should we go with your other option of demoting WARNING to pr_err
then? I don't how many real bugs that warning caught versus callers
just properly handle EEXIST.

[Cluster-devel] WARNING: kobject bug in sysfs_warn_dup

[Greg KH]

On Thu, Apr 05, 2018 at 10:00:04AM +0100, Steven Whitehouse wrote:
> Hi,
> 
> 
> On 05/04/18 09:52, Dmitry Vyukov wrote:
> > On Thu, Apr 5, 2018 at 10:36 AM, Steven Whitehouse <swhiteho@redhat.com> wrote:
> > > Hi,
> > > 
> > > 
> > > 
> > > On 05/04/18 09:19, Dmitry Vyukov wrote:
> > > > On Thu, Apr 5, 2018 at 8:34 AM, Greg KH <gregkh@linuxfoundation.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 at 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.

thanks,

greg k-h

[Cluster-devel] WARNING: kobject bug in sysfs_warn_dup

[Steven Whitehouse]

Hi,


On 05/04/18 14:34, Greg KH wrote:
> On Thu, Apr 05, 2018 at 10:00:04AM +0100, Steven Whitehouse wrote:
>> Hi,
>>
>>
>> On 05/04/18 09:52, Dmitry Vyukov wrote:
>>> On Thu, Apr 5, 2018 at 10:36 AM, Steven Whitehouse <swhiteho@redhat.com> wrote:
>>>> Hi,
>>>>
>>>>
>>>>
>>>> On 05/04/18 09:19, Dmitry Vyukov wrote:
>>>>> On Thu, Apr 5, 2018 at 8:34 AM, Greg KH <gregkh@linuxfoundation.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 at 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.
>
> thanks,
>
> greg k-h

Unfortunately, no. We don't have the list of names elsewhere. The names 
are used as a cluster-wide ID, so not having duplicates on a single node 
is a good thing :-) The name is effectively the same as the fs label. We 
could create a list - while sysfs does the job for us, we've not needed 
to do that though,

Steve.

[Cluster-devel] WARNING: kobject bug in sysfs_warn_dup

[Dmitry Vyukov]

On Thu, Apr 5, 2018 at 3:34 PM, Greg KH <gregkh@linuxfoundation.org> wrote:
> On Thu, Apr 05, 2018 at 10:00:04AM +0100, Steven Whitehouse wrote:
>> Hi,
>>
>>
>> On 05/04/18 09:52, Dmitry Vyukov wrote:
>> > On Thu, Apr 5, 2018 at 10:36 AM, Steven Whitehouse <swhiteho@redhat.com> wrote:
>> > > Hi,
>> > >
>> > >
>> > >
>> > > On 05/04/18 09:19, Dmitry Vyukov wrote:
>> > > > On Thu, Apr 5, 2018 at 8:34 AM, Greg KH <gregkh@linuxfoundation.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 at 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));

[Cluster-devel] WARNING: kobject bug in sysfs_warn_dup

[Greg KH]

On Thu, Apr 05, 2018 at 03:59:58PM +0200, Dmitry Vyukov wrote:
> On Thu, Apr 5, 2018 at 3:34 PM, Greg KH <gregkh@linuxfoundation.org> wrote:
> > On Thu, Apr 05, 2018 at 10:00:04AM +0100, Steven Whitehouse wrote:
> >> Hi,
> >>
> >>
> >> On 05/04/18 09:52, Dmitry Vyukov wrote:
> >> > On Thu, Apr 5, 2018 at 10:36 AM, Steven Whitehouse <swhiteho@redhat.com> wrote:
> >> > > Hi,
> >> > >
> >> > >
> >> > >
> >> > > On 05/04/18 09:19, Dmitry Vyukov wrote:
> >> > > > On Thu, Apr 5, 2018 at 8:34 AM, Greg KH <gregkh@linuxfoundation.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 at 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?

thanks,

greg k-h

[Cluster-devel] WARNING: kobject bug in sysfs_warn_dup

[Dmitry Vyukov]

On Thu, Apr 5, 2018 at 4:23 PM, Greg KH <gregkh@linuxfoundation.org> wrote:
>> >> On 05/04/18 09:52, Dmitry Vyukov wrote:
>> >> > On Thu, Apr 5, 2018 at 10:36 AM, Steven Whitehouse <swhiteho@redhat.com> wrote:
>> >> > > Hi,
>> >> > >
>> >> > >
>> >> > >
>> >> > > On 05/04/18 09:19, Dmitry Vyukov wrote:
>> >> > > > On Thu, Apr 5, 2018 at 8:34 AM, Greg KH <gregkh@linuxfoundation.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 at 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.

[Cluster-devel] WARNING: kobject bug in sysfs_warn_dup

[Dmitry Vyukov]

On Wed, Apr 11, 2018 at 5:04 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
> On Thu, Apr 5, 2018 at 4:23 PM, Greg KH <gregkh@linuxfoundation.org> wrote:
>>> >> On 05/04/18 09:52, Dmitry Vyukov wrote:
>>> >> > On Thu, Apr 5, 2018 at 10:36 AM, Steven Whitehouse <swhiteho@redhat.com> wrote:
>>> >> > > Hi,
>>> >> > >
>>> >> > >
>>> >> > >
>>> >> > > On 05/04/18 09:19, Dmitry Vyukov wrote:
>>> >> > > > On Thu, Apr 5, 2018 at 8:34 AM, Greg KH <gregkh@linuxfoundation.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 at 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?

Wait, it's the other way around.
I've already mailed a patch that does s/WARN/pr_err/. But can remove
it entirely, whichever you prefer.

> 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.