WARNING: locking bug in __kernfs_remove

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 4ccc9e2db7ac Add linux-next specific files for 20210729
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=144b592a300000
kernel config: https://syzkaller.appspot.com/x/.config?x=75a5bed89b5c0fd2
dashboard link: https://syzkaller.appspot.com/bug?extid=f221f6501d8c15fb0914
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
CC: [gre...@linuxfoundation.org linux-...@vger.kernel.org t...@kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f221f6...@syzkaller.appspotmail.com

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WARNING: CPU: 1 PID: 23042 at kernel/locking/lockdep.c:897 look_up_lock_class+0x6a/0xd0 kernel/locking/lockdep.c:897
Modules linked in:
CPU: 1 PID: 23042 Comm: kworker/u4:1 Not tainted 5.14.0-rc3-next-20210729-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: netns cleanup_net
RIP: 0010:look_up_lock_class+0x6a/0xd0 kernel/locking/lockdep.c:897
Code: 85 c0 75 0a eb 57 48 8b 00 48 85 c0 74 4f 48 39 70 40 75 f2 48 8b 4f 18 48 39 88 b0 00 00 00 74 0b 48 81 3f c0 03 ee 8e 74 02 <0f> 0b 5d c3 9c 5a 80 e6 02 74 c2 e8 d6 9e a4 fa 85 c0 74 1f 8b 05
RSP: 0018:ffffc9000b88f548 EFLAGS: 00010083
RAX: ffffffff8fcf9280 RBX: ffffffff9022a7e0 RCX: 0000000000000000
RDX: 0000000000000046 RSI: ffffffff8c44c5f8 RDI: ffff888000116e88
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888000116e88
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffd73bd1ff8 CR3: 000000002b268000 CR4: 00000000001526e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
register_lock_class+0xb7/0x10c0 kernel/locking/lockdep.c:1246
__lock_acquire+0x105/0x54a0 kernel/locking/lockdep.c:4894
lock_acquire kernel/locking/lockdep.c:5625 [inline]
lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5590
kernfs_drain fs/kernfs/dir.c:470 [inline]
__kernfs_remove+0x887/0xab0 fs/kernfs/dir.c:1339
kernfs_remove_by_name_ns+0x4f/0xa0 fs/kernfs/dir.c:1532
sysfs_remove_file include/linux/sysfs.h:613 [inline]
device_remove_file drivers/base/core.c:2741 [inline]
device_del+0x4ed/0xd60 drivers/base/core.c:3541
unregister_netdevice_many+0xd21/0x1790 net/core/dev.c:11123
vti6_exit_batch_net+0x3a0/0x670 net/ipv6/ip6_vti.c:1188
ops_exit_list+0x10d/0x160 net/core/net_namespace.c:178
cleanup_net+0x4ea/0xb10 net/core/net_namespace.c:595
process_one_work+0x98d/0x1630 kernel/workqueue.c:2276
worker_thread+0x658/0x11f0 kernel/workqueue.c:2422
kthread+0x3e5/0x4d0 kernel/kthread.c:319
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.