Messages in this thread |  | | Subject | Re: WARNING: kobject bug in sysfs_warn_dup | From | Steven Whitehouse <> | Date | Thu, 5 Apr 2018 14:43:43 +0100 |
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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@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.
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