Messages in this thread | | | From | Dmitry Vyukov <> | Date | Wed, 11 Apr 2018 17:28:00 +0200 | Subject | Re: WARNING: kobject bug in sysfs_warn_dup |
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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@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.
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