INFO: task hung in kernfs_remove

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: c555efaf Linux 4.19.84
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=13d779e6e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=9140f2df4ddc6016
dashboard link: https://syzkaller.appspot.com/bug?extid=e01da8bd2a979fec9a7d
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+e01da8...@syzkaller.appspotmail.com

RDX: 0000000000000004 RSI: 00007ffc69eb6930 RDI: 0000000000000007
RBP: 0000000000625500 R08: 00007ffc69ec4000 R09: 000001003f6f3638
R10: 000000000000edf7 R11: 0000000000000246 R12: 00000000022353f0
R13: 00007ffc69eb7987 R14: 0000000000000005 R15: 00000000021a2030
INFO: task kworker/u4:0:7 blocked for more than 140 seconds.
Not tainted 4.19.84 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:0 D24960 7 2 0x80000000
Workqueue: netns cleanup_net
Call Trace:
context_switch kernel/sched/core.c:2826 [inline]
__schedule+0x866/0x1dc0 kernel/sched/core.c:3515
schedule+0x92/0x1c0 kernel/sched/core.c:3559
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3617
__mutex_lock_common kernel/locking/mutex.c:1002 [inline]
__mutex_lock+0x726/0x1300 kernel/locking/mutex.c:1072
Mem-Info:
active_anon:1356840 inactive_anon:255 isolated_anon:0
active_file:40 inactive_file:90 isolated_file:28
unevictable:0 dirty:0 writeback:0 unstable:0
slab_reclaimable:14542 slab_unreclaimable:117160
mapped:52299 shmem:325 pagetables:8874 bounce:0
free:24964 free_pcp:0 free_cma:0
Node 0 active_anon:1729884kB inactive_anon:1020kB active_file:84kB
inactive_file:444kB unevictable:0kB isolated(anon):0kB isolated(file):96kB
mapped:209320kB dirty:0kB writeback:0kB shmem:1300kB shmem_thp: 0kB
shmem_pmdmapped: 0kB anon_thp: 98304kB writeback_tmp:0kB unstable:0kB
all_unreclaimable? no
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
kernfs_remove+0x1c/0x40 fs/kernfs/dir.c:1351
sysfs_remove_dir+0xd2/0x110 fs/sysfs/dir.c:101
kobject_del.part.0+0x3a/0xf0 lib/kobject.c:592
kobject_del lib/kobject.c:588 [inline]
kobject_cleanup lib/kobject.c:656 [inline]
kobject_release lib/kobject.c:691 [inline]
kref_put include/linux/kref.h:70 [inline]
kobject_put.cold+0x1f9/0x2e6 lib/kobject.c:708
net_rx_queue_update_kobjects+0x361/0x480 net/core/net-sysfs.c:979
Node 1 active_anon:3697476kB inactive_anon:0kB active_file:0kB
inactive_file:4kB unevictable:0kB isolated(anon):0kB isolated(file):0kB
mapped:0kB dirty:0kB writeback:0kB shmem:0kB shmem_thp: 0kB
shmem_pmdmapped: 0kB anon_thp: 0kB writeback_tmp:0kB unstable:0kB
all_unreclaimable? yes
Node 0 DMA free:10440kB min:220kB low:272kB high:324kB active_anon:5396kB
inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB
writepending:0kB present:15992kB managed:15908kB mlocked:0kB
kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB
free_cma:0kB
lowmem_reserve[]: 0 2555 2557 2557
remove_queue_kobjects net/core/net-sysfs.c:1567 [inline]
netdev_unregister_kobject+0x155/0x1f0 net/core/net-sysfs.c:1718
Node 0 DMA32 free:35800kB min:36248kB low:45308kB high:54368kB
active_anon:1724500kB inactive_anon:1020kB active_file:124kB
inactive_file:240kB unevictable:0kB writepending:0kB present:3129332kB
managed:2619976kB mlocked:0kB kernel_stack:15488kB pagetables:18528kB
bounce:0kB free_pcp:616kB local_pcp:440kB free_cma:0kB
rollback_registered_many+0x6bb/0xda0 net/core/dev.c:8029
lowmem_reserve[]: 0 0 2 2
Node 0 Normal free:8kB min:32kB low:40kB high:48kB active_anon:0kB
inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB
writepending:0kB present:786432kB managed:2428kB mlocked:0kB
kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB
free_cma:0kB


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[syzbot]

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