INFO: task hung in unregister_netdevice_notifier

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
17dec0a949153d9ac00760ba2f5b78cb583e995f (Wed Apr 4 02:15:32 2018 +0000)
Merge branch 'userns-linus' of
git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace
syzbot dashboard link:
https://syzkaller.appspot.com/bug?extid=fa492afaefcbd0cfc06a

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:
https://syzkaller.appspot.com/x/log.txt?id=4662290540396544
Kernel config:
https://syzkaller.appspot.com/x/.config?id=9118669095563550941
compiler: gcc (GCC) 7.1.1 20170620
CC: [da...@davemloft.net linu...@vger.kernel.org
linux-...@vger.kernel.org m...@pengutronix.de net...@vger.kernel.org
sock...@hartkopp.net]

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+fa492a...@syzkaller.appspotmail.com
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details.
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unregister_netdevice: waiting for lo to become free. Usage count = 3
unregister_netdevice: waiting for lo to become free. Usage count = 3
unregister_netdevice: waiting for lo to become free. Usage count = 3
unregister_netdevice: waiting for lo to become free. Usage count = 3
unregister_netdevice: waiting for lo to become free. Usage count = 3
INFO: task syz-executor0:18481 blocked for more than 120 seconds.
Not tainted 4.16.0+ #14
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0 D21552 18481 7939 0x80000002
Call Trace:
context_switch kernel/sched/core.c:2848 [inline]
__schedule+0x8fb/0x1ef0 kernel/sched/core.c:3490
schedule+0xf5/0x430 kernel/sched/core.c:3549
__rwsem_down_write_failed_common+0x85b/0x15f0
kernel/locking/rwsem-xadd.c:566
rwsem_down_write_failed+0xe/0x10 kernel/locking/rwsem-xadd.c:595
call_rwsem_down_write_failed+0x17/0x30 arch/x86/lib/rwsem.S:117
__down_write arch/x86/include/asm/rwsem.h:142 [inline]
down_write+0xa2/0x120 kernel/locking/rwsem.c:72
unregister_netdevice_notifier+0x98/0x500 net/core/dev.c:1698
bcm_release+0x93/0x5d0 net/can/bcm.c:1507
sock_release+0x8d/0x1e0 net/socket.c:594
sock_close+0x16/0x20 net/socket.c:1149
__fput+0x327/0x7f0 fs/file_table.c:209
____fput+0x15/0x20 fs/file_table.c:243
task_work_run+0x1ab/0x280 kernel/task_work.c:113
exit_task_work include/linux/task_work.h:22 [inline]
do_exit+0x1986/0x2700 kernel/exit.c:865
do_group_exit+0x149/0x400 kernel/exit.c:968
get_signal+0x74c/0x16e0 kernel/signal.c:2469
do_signal+0x90/0x1e90 arch/x86/kernel/signal.c:810
exit_to_usermode_loop+0x258/0x2f0 arch/x86/entry/common.c:162
prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
syscall_return_slowpath arch/x86/entry/common.c:265 [inline]
do_syscall_64+0x6ec/0x940 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4552d9
RSP: 002b:00007f79e0415ce8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 000000000072bf80 RCX: 00000000004552d9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000000072bf80
RBP: 000000000072bf80 R08: 0000000000000000 R09: 000000000072bf58
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fff2fb9abdf R14: 00007f79e04169c0 R15: 0000000000000001

Showing all locks held in the system:
4 locks held by kworker/u4:4/220:
#0: 00000000b2c5b7e0 ((wq_completion)"%s""netns"){+.+.}, at:
__write_once_size include/linux/compiler.h:215 [inline]
#0: 00000000b2c5b7e0 ((wq_completion)"%s""netns"){+.+.}, at:
arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: 00000000b2c5b7e0 ((wq_completion)"%s""netns"){+.+.}, at: atomic64_set
include/asm-generic/atomic-instrumented.h:40 [inline]
#0: 00000000b2c5b7e0 ((wq_completion)"%s""netns"){+.+.}, at:
atomic_long_set include/asm-generic/atomic-long.h:57 [inline]
#0: 00000000b2c5b7e0 ((wq_completion)"%s""netns"){+.+.}, at: set_work_data
kernel/workqueue.c:617 [inline]
#0: 00000000b2c5b7e0 ((wq_completion)"%s""netns"){+.+.}, at:
set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
#0: 00000000b2c5b7e0 ((wq_completion)"%s""netns"){+.+.}, at:
process_one_work+0xb83/0x1c40 kernel/workqueue.c:2116
#1: 000000005bddcf94 (net_cleanup_work){+.+.}, at:
process_one_work+0xbd9/0x1c40 kernel/workqueue.c:2120
#2: 00000000bcb85d3e (pernet_ops_rwsem){++++}, at: cleanup_net+0x11b/0xaa0
net/core/net_namespace.c:490
#3: 000000003224c213 (rcu_sched_state.barrier_mutex){+.+.}, at:
_rcu_barrier+0x142/0x770 kernel/rcu/tree.c:3495
2 locks held by khungtaskd/879:
#0: 00000000ee7627a2 (rcu_read_lock){....}, at:
check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
#0: 00000000ee7627a2 (rcu_read_lock){....}, at: watchdog+0x1d6/0xd70
kernel/hung_task.c:249
#1: 0000000026a374dc (tasklist_lock){.+.+}, at:
debug_show_all_locks+0xd3/0x3d0 kernel/locking/lockdep.c:4470
1 lock held by rsyslogd/4271:
#0: 000000008d9687f4 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x165/0x1a0
fs/file.c:766
2 locks held by getty/4361:
#0: 0000000099c16698 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000b76e1a7f (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4362:
#0: 0000000055a2ecd9 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 000000006e848075 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4363:
#0: 00000000b32a05f7 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 000000000a826405 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4364:
#0: 000000003b57022d (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 000000006d615b00 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4365:
#0: 000000004ef877b6 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000aa8cf8ce (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4366:
#0: 0000000069fa310f (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000604ab6fd (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4367:
#0: 000000003a1076a3 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000ab341c8e (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
1 lock held by syz-executor0/18481:
#0: 00000000bcb85d3e (pernet_ops_rwsem){++++}, at:
unregister_netdevice_notifier+0x98/0x500 net/core/dev.c:1698
1 lock held by syz-executor4/18492:
#0: 00000000bcb85d3e (pernet_ops_rwsem){++++}, at:
register_netdevice_notifier+0xb4/0x870 net/core/dev.c:1629
1 lock held by syz-executor4/18510:
#0: 00000000bcb85d3e (pernet_ops_rwsem){++++}, at:
register_netdevice_notifier+0xb4/0x870 net/core/dev.c:1629
1 lock held by syz-executor0/18518:
#0: 00000000bcb85d3e (pernet_ops_rwsem){++++}, at: copy_net_ns+0x28d/0x480
net/core/net_namespace.c:432

=============================================

NMI backtrace for cpu 0
CPU: 0 PID: 879 Comm: khungtaskd Not tainted 4.16.0+ #14
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
nmi_cpu_backtrace+0x1e0/0x220 lib/nmi_backtrace.c:103
nmi_trigger_cpumask_backtrace+0x123/0x180 lib/nmi_backtrace.c:62
arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
trigger_all_cpu_backtrace include/linux/nmi.h:138 [inline]
check_hung_task kernel/hung_task.c:132 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:190 [inline]
watchdog+0x969/0xd70 kernel/hung_task.c:249
kthread+0x33c/0x400 kernel/kthread.c:238
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:411
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.16.0+ #14
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:tick_do_update_jiffies64 kernel/time/tick-sched.c:65 [inline]
RIP: 0010:tick_nohz_update_jiffies kernel/time/tick-sched.c:495 [inline]
RIP: 0010:tick_nohz_irq_enter kernel/time/tick-sched.c:1128 [inline]
RIP: 0010:tick_irq_enter+0x1bf/0x390 kernel/time/tick-sched.c:1145
RSP: 0018:ffff8801db107ca8 EFLAGS: 00000002
RAX: dffffc0000000000 RBX: 0000000000000093 RCX: 0000000000000000
RDX: ffffffff89e090a0 RSI: 0000000000000000 RDI: ffffffff89e090a0
RBP: ffff8801db107cc8 R08: ffffed003b625a05 R09: ffffed003b625a05
R10: 0000000000000001 R11: ffffed003b625a04 R12: 0000000000058f01
R13: ffff8801db126560 R14: 000000564ffffe41 R15: 0000000000000001
FS: 0000000000000000(0000) GS:ffff8801db100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffff600400 CR3: 00000001c3cb1000 CR4: 00000000001406e0
DR0: 0000000020000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Call Trace:
<IRQ>
irq_enter+0xb6/0xd0 kernel/softirq.c:346
scheduler_ipi+0x317/0xa40 kernel/sched/core.c:1768
smp_reschedule_interrupt+0xe6/0x650 arch/x86/kernel/smp.c:277
reschedule_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:886
</IRQ>
RIP: 0010:native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:54
RSP: 0018:ffff8801d9ecfcb0 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff02
RAX: dffffc0000000000 RBX: 1ffff1003b3d9f99 RCX: 0000000000000000
RDX: 1ffffffff10a2558 RSI: 0000000000000001 RDI: ffffffff88512ac0
RBP: ffff8801d9ecfcb0 R08: ffffed003b6246c3 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
R13: ffff8801d9ecfd68 R14: ffffffff88ee1460 R15: 0000000000000000
arch_safe_halt arch/x86/include/asm/paravirt.h:94 [inline]
default_idle+0xbf/0x430 arch/x86/kernel/process.c:354
arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:345
default_idle_call+0x36/0x90 kernel/sched/idle.c:93
cpuidle_idle_call kernel/sched/idle.c:151 [inline]
do_idle+0x24a/0x3b0 kernel/sched/idle.c:241
cpu_startup_entry+0x104/0x120 kernel/sched/idle.c:346
start_secondary+0x40a/0x590 arch/x86/kernel/smpboot.c:267
secondary_startup_64+0xa5/0xb0 arch/x86/kernel/head_64.S:242
Code: 00 fa 66 0f 1f 44 00 00 e8 7f 65 f1 ff 48 c7 c7 a0 90 e0 89 48 b8 00
00 00 00 00 fc ff df 4d 89 f4 48 89 fa 4c 2b 25 31 2d 7b 08 <48> c1 ea 03
80 3c 02 00 0f 85 a4 01 00 00 4c 3b 25 bc 29 7b 08


---
This bug is generated by a dumb bot. It may contain errors.
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[Dmitry Vyukov]

This is now superseded by "unregister_netdevice: waiting for DEV to
become free":
https://syzkaller.appspot.com/bug?id=1a97a5bd119fd97995f752819fd87840ab9479a9

#syz invalid

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