Messages in this thread |  | | Subject | Re: WARNING: kobject bug in sysfs_warn_dup | From | Steven Whitehouse <> | Date | Thu, 5 Apr 2018 10:00:04 +0100 |
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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. 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.
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