Re: INFO: task hung in cleanup_net

Re: INFO: task hung in cleanup_net

[Dmitry Vyukov]

On Tue, Dec 19, 2017 at 1:33 PM, syzbot
<bot+b17f10c8a8c693b40723d40d6553fbc54d197679@syzkaller.appspotmail.com>
wrote:
> Hello,
>
> syzkaller hit the following crash on
> e40fd8d6b4d9f59b160faa1736f78fc07533ff37
> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
>
> Unfortunately, I don't have any reproducer for this bug yet.
>
>
> sctp: sctp_transport_update_pmtu: Reported pmtu 508 too low, using default
> minimum of 512
> sctp: sctp_transport_update_pmtu: Reported pmtu 508 too low, using default
> minimum of 512
> sctp: sctp_transport_update_pmtu: Reported pmtu 508 too low, using default
> minimum of 512
> INFO: task kworker/u4:11:3785 blocked for more than 120 seconds.
>       Not tainted 4.15.0-rc2-next-20171207+ #61
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> kworker/u4:11   D16448  3785      2 0x80000000
> Workqueue: netns cleanup_net
> Call Trace:
>  context_switch kernel/sched/core.c:2800 [inline]
>  __schedule+0x8eb/0x2060 kernel/sched/core.c:3376
>  schedule+0xf5/0x430 kernel/sched/core.c:3435
>  schedule_preempt_disabled+0x10/0x20 kernel/sched/core.c:3493
>  __mutex_lock_common kernel/locking/mutex.c:833 [inline]
>  __mutex_lock+0xaad/0x1a80 kernel/locking/mutex.c:893
>  mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
>  rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74
>  cleanup_net+0x24c/0xb60 net/core/net_namespace.c:453
>  process_one_work+0xbfd/0x1bc0 kernel/workqueue.c:2113
>  worker_thread+0x223/0x1990 kernel/workqueue.c:2247
>  kthread+0x37a/0x440 kernel/kthread.c:238
>  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:524
>
> Showing all locks held in the system:
> 2 locks held by khungtaskd/672:
>  #0:  (rcu_read_lock){....}, at: [<00000000b9bef8ab>]
> check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
>  #0:  (rcu_read_lock){....}, at: [<00000000b9bef8ab>] watchdog+0x1c5/0xd60
> kernel/hung_task.c:249
>  #1:  (tasklist_lock){.+.+}, at: [<000000006d6acf8b>]
> debug_show_all_locks+0xd3/0x400 kernel/locking/lockdep.c:4554
> 1 lock held by rsyslogd/2970:
>  #0:  (&f->f_pos_lock){+.+.}, at: [<000000001cede688>]
> __fdget_pos+0x131/0x1a0 fs/file.c:765
> 2 locks held by getty/3052:
>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3053:
>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3054:
>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3055:
>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3056:
>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3057:
>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3058:
>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 1 lock held by syz-executor2/3320:
>  #0:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
> net/core/rtnetlink.c:74
> 4 locks held by kworker/u4:11/3785:
>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
> __write_once_size include/linux/compiler.h:212 [inline]
>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
> atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
> atomic_long_set include/asm-generic/atomic-long.h:57 [inline]
>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
> set_work_data kernel/workqueue.c:619 [inline]
>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
> set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline]
>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
> process_one_work+0xad4/0x1bc0 kernel/workqueue.c:2084
>  #1:  (net_cleanup_work){+.+.}, at: [<000000008a817b5c>]
> process_one_work+0xb2f/0x1bc0 kernel/workqueue.c:2088
>  #2:  (net_mutex){+.+.}, at: [<0000000079150fd8>] cleanup_net+0x247/0xb60
> net/core/net_namespace.c:450
>  #3:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
> net/core/rtnetlink.c:74
> 3 locks held by kworker/0:6/14978:
>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
> __write_once_size include/linux/compiler.h:212 [inline]
>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
> atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
> atomic_long_set include/asm-generic/atomic-long.h:57 [inline]
>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
> set_work_data kernel/workqueue.c:619 [inline]
>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
> set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline]
>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
> process_one_work+0xad4/0x1bc0 kernel/workqueue.c:2084
>  #1:  ((addr_chk_work).work){+.+.}, at: [<000000008a817b5c>]
> process_one_work+0xb2f/0x1bc0 kernel/workqueue.c:2088
>  #2:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
> net/core/rtnetlink.c:74
> 1 lock held by syz-executor2/15852:
>  #0:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
> net/core/rtnetlink.c:74
> 1 lock held by syz-executor7/15958:
>  #0:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
> net/core/rtnetlink.c:74
> 1 lock held by syz-executor7/15961:
>  #0:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
> net/core/rtnetlink.c:74
>
> =============================================
>
> NMI backtrace for cpu 1
> CPU: 1 PID: 672 Comm: khungtaskd Not tainted 4.15.0-rc2-next-20171207+ #61
> 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+0x194/0x257 lib/dump_stack.c:53
>  nmi_cpu_backtrace+0x1d2/0x210 lib/nmi_backtrace.c:103
>  nmi_trigger_cpumask_backtrace+0x122/0x180 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+0x90c/0xd60 kernel/hung_task.c:249
>  kthread+0x37a/0x440 kernel/kthread.c:238
>  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:524
> Sending NMI from CPU 1 to CPUs 0:
> NMI backtrace for cpu 0
> CPU: 0 PID: 15938 Comm: syz-executor7 Not tainted 4.15.0-rc2-next-20171207+
> #61
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:inb arch/x86/include/asm/io.h:348 [inline]
> RIP: 0010:io_serial_in+0x6b/0x90 drivers/tty/serial/8250/8250_port.c:434
> RSP: 0018:ffff8801c1c173e8 EFLAGS: 00000002
> RAX: dffffc0000000000 RBX: 00000000000003fd RCX: 0000000000000000
> RDX: 00000000000003fd RSI: ffffc90001c88000 RDI: ffffffff880fa9c0
> RBP: ffff8801c1c173f8 R08: 0000000000000002 R09: 000000000000000c
> R10: 0000000000000000 R11: ffffffff87896d20 R12: ffffffff880fa980
> R13: 0000000000000020 R14: fffffbfff101f577 R15: fffffbfff101f53a
> FS:  00007f1ef8fad700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fbea91b6000 CR3: 00000001d0aaa000 CR4: 00000000001406f0
> DR0: 0000000020001000 DR1: 0000000020001000 DR2: 0000000020001020
> DR3: 0000000020000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
> Call Trace:
>  serial_in drivers/tty/serial/8250/8250.h:111 [inline]
>  wait_for_xmitr+0x93/0x1e0 drivers/tty/serial/8250/8250_port.c:2033
>  serial8250_console_putchar+0x1f/0x60
> drivers/tty/serial/8250/8250_port.c:3170
>  uart_console_write+0xac/0xe0 drivers/tty/serial/serial_core.c:1858
>  serial8250_console_write+0x647/0xa20
> drivers/tty/serial/8250/8250_port.c:3236
>  univ8250_console_write+0x5f/0x70 drivers/tty/serial/8250/8250_core.c:590
>  call_console_drivers kernel/printk/printk.c:1574 [inline]
>  console_unlock+0x788/0xd70 kernel/printk/printk.c:2233
>  vprintk_emit+0x4ad/0x590 kernel/printk/printk.c:1757
>  vprintk_default+0x28/0x30 kernel/printk/printk.c:1796
>  vprintk_func+0x57/0xc0 kernel/printk/printk_safe.c:379
>  printk+0xaa/0xca kernel/printk/printk.c:1829
>  __dev_set_promiscuity+0x2a4/0x630 net/core/dev.c:6609
>  __dev_change_flags+0x559/0x990 net/core/dev.c:6826
>  dev_change_flags+0x88/0x140 net/core/dev.c:6886
>  dev_ifsioc+0x60d/0x9b0 net/core/dev_ioctl.c:257
>  dev_ioctl+0x2c2/0xf90 net/core/dev_ioctl.c:566
>  sock_do_ioctl+0x94/0xb0 net/socket.c:971
>  sock_ioctl+0x2c2/0x440 net/socket.c:1061
>  vfs_ioctl fs/ioctl.c:46 [inline]
>  do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:686
>  SYSC_ioctl fs/ioctl.c:701 [inline]
>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
>  entry_SYSCALL_64_fastpath+0x1f/0x96
> RIP: 0033:0x452a39
> RSP: 002b:00007f1ef8facc58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007f1ef8fad700 RCX: 0000000000452a39
> RDX: 00000000208a3fe0 RSI: 0000000000008914 RDI: 0000000000000019
> RBP: 0000000000a6f880 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000212 R12: 0000000000000000
> R13: 0000000000a6f7ff R14: 00007f1ef8fad9c0 R15: 0000000000000002
> Code: 24 d9 00 00 00 49 8d 7c 24 40 48 b8 00 00 00 00 00 fc ff df 48 89 fa
> 48 c1 ea 03 d3 e3 80 3c 02 00 75 17 41 03 5c 24 40 89 da ec <5b> 0f b6 c0 41
> 5c 5d c3 e8 88 ad 18 ff eb c2 e8 e1 ad 18 ff eb


This looks like +rtnetlink issue.

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Re: INFO: task hung in cleanup_net

[David Ahern]

On 12/19/17 5:47 AM, Dmitry Vyukov wrote:
> On Tue, Dec 19, 2017 at 1:33 PM, syzbot
> <bot+b17f10c8a8c693b40723d40d6553fbc54d197679@syzkaller.appspotmail.com>
> wrote:
>> Hello,
>>
>> syzkaller hit the following crash on
>> e40fd8d6b4d9f59b160faa1736f78fc07533ff37
>> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
>> compiler: gcc (GCC) 7.1.1 20170620
>> .config is attached
>> Raw console output is attached.
>>
>> Unfortunately, I don't have any reproducer for this bug yet.
>>
>>
>> sctp: sctp_transport_update_pmtu: Reported pmtu 508 too low, using default
>> minimum of 512
>> sctp: sctp_transport_update_pmtu: Reported pmtu 508 too low, using default
>> minimum of 512
>> sctp: sctp_transport_update_pmtu: Reported pmtu 508 too low, using default
>> minimum of 512
>> INFO: task kworker/u4:11:3785 blocked for more than 120 seconds.
>>       Not tainted 4.15.0-rc2-next-20171207+ #61
>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> kworker/u4:11   D16448  3785      2 0x80000000
>> Workqueue: netns cleanup_net
>> Call Trace:
>>  context_switch kernel/sched/core.c:2800 [inline]
>>  __schedule+0x8eb/0x2060 kernel/sched/core.c:3376
>>  schedule+0xf5/0x430 kernel/sched/core.c:3435
>>  schedule_preempt_disabled+0x10/0x20 kernel/sched/core.c:3493
>>  __mutex_lock_common kernel/locking/mutex.c:833 [inline]
>>  __mutex_lock+0xaad/0x1a80 kernel/locking/mutex.c:893
>>  mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
>>  rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74
>>  cleanup_net+0x24c/0xb60 net/core/net_namespace.c:453
>>  process_one_work+0xbfd/0x1bc0 kernel/workqueue.c:2113
>>  worker_thread+0x223/0x1990 kernel/workqueue.c:2247
>>  kthread+0x37a/0x440 kernel/kthread.c:238
>>  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:524
>>
>> Showing all locks held in the system:
>> 2 locks held by khungtaskd/672:
>>  #0:  (rcu_read_lock){....}, at: [<00000000b9bef8ab>]
>> check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
>>  #0:  (rcu_read_lock){....}, at: [<00000000b9bef8ab>] watchdog+0x1c5/0xd60
>> kernel/hung_task.c:249
>>  #1:  (tasklist_lock){.+.+}, at: [<000000006d6acf8b>]
>> debug_show_all_locks+0xd3/0x400 kernel/locking/lockdep.c:4554
>> 1 lock held by rsyslogd/2970:
>>  #0:  (&f->f_pos_lock){+.+.}, at: [<000000001cede688>]
>> __fdget_pos+0x131/0x1a0 fs/file.c:765
>> 2 locks held by getty/3052:
>>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
>> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
>> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
>> 2 locks held by getty/3053:
>>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
>> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
>> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
>> 2 locks held by getty/3054:
>>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
>> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
>> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
>> 2 locks held by getty/3055:
>>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
>> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
>> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
>> 2 locks held by getty/3056:
>>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
>> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
>> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
>> 2 locks held by getty/3057:
>>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
>> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
>> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
>> 2 locks held by getty/3058:
>>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
>> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
>> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
>> 1 lock held by syz-executor2/3320:
>>  #0:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
>> net/core/rtnetlink.c:74
>> 4 locks held by kworker/u4:11/3785:
>>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
>> __write_once_size include/linux/compiler.h:212 [inline]
>>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
>> atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
>>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
>> atomic_long_set include/asm-generic/atomic-long.h:57 [inline]
>>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
>> set_work_data kernel/workqueue.c:619 [inline]
>>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
>> set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline]
>>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
>> process_one_work+0xad4/0x1bc0 kernel/workqueue.c:2084
>>  #1:  (net_cleanup_work){+.+.}, at: [<000000008a817b5c>]
>> process_one_work+0xb2f/0x1bc0 kernel/workqueue.c:2088
>>  #2:  (net_mutex){+.+.}, at: [<0000000079150fd8>] cleanup_net+0x247/0xb60
>> net/core/net_namespace.c:450
>>  #3:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
>> net/core/rtnetlink.c:74
>> 3 locks held by kworker/0:6/14978:
>>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
>> __write_once_size include/linux/compiler.h:212 [inline]
>>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
>> atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
>>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
>> atomic_long_set include/asm-generic/atomic-long.h:57 [inline]
>>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
>> set_work_data kernel/workqueue.c:619 [inline]
>>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
>> set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline]
>>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
>> process_one_work+0xad4/0x1bc0 kernel/workqueue.c:2084
>>  #1:  ((addr_chk_work).work){+.+.}, at: [<000000008a817b5c>]
>> process_one_work+0xb2f/0x1bc0 kernel/workqueue.c:2088
>>  #2:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
>> net/core/rtnetlink.c:74
>> 1 lock held by syz-executor2/15852:
>>  #0:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
>> net/core/rtnetlink.c:74
>> 1 lock held by syz-executor7/15958:
>>  #0:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
>> net/core/rtnetlink.c:74
>> 1 lock held by syz-executor7/15961:
>>  #0:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
>> net/core/rtnetlink.c:74
>>
>> =============================================
>>
>> NMI backtrace for cpu 1
>> CPU: 1 PID: 672 Comm: khungtaskd Not tainted 4.15.0-rc2-next-20171207+ #61
>> 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+0x194/0x257 lib/dump_stack.c:53
>>  nmi_cpu_backtrace+0x1d2/0x210 lib/nmi_backtrace.c:103
>>  nmi_trigger_cpumask_backtrace+0x122/0x180 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+0x90c/0xd60 kernel/hung_task.c:249
>>  kthread+0x37a/0x440 kernel/kthread.c:238
>>  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:524
>> Sending NMI from CPU 1 to CPUs 0:
>> NMI backtrace for cpu 0
>> CPU: 0 PID: 15938 Comm: syz-executor7 Not tainted 4.15.0-rc2-next-20171207+
>> #61
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>> Google 01/01/2011
>> RIP: 0010:inb arch/x86/include/asm/io.h:348 [inline]
>> RIP: 0010:io_serial_in+0x6b/0x90 drivers/tty/serial/8250/8250_port.c:434
>> RSP: 0018:ffff8801c1c173e8 EFLAGS: 00000002
>> RAX: dffffc0000000000 RBX: 00000000000003fd RCX: 0000000000000000
>> RDX: 00000000000003fd RSI: ffffc90001c88000 RDI: ffffffff880fa9c0
>> RBP: ffff8801c1c173f8 R08: 0000000000000002 R09: 000000000000000c
>> R10: 0000000000000000 R11: ffffffff87896d20 R12: ffffffff880fa980
>> R13: 0000000000000020 R14: fffffbfff101f577 R15: fffffbfff101f53a
>> FS:  00007f1ef8fad700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007fbea91b6000 CR3: 00000001d0aaa000 CR4: 00000000001406f0
>> DR0: 0000000020001000 DR1: 0000000020001000 DR2: 0000000020001020
>> DR3: 0000000020000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
>> Call Trace:
>>  serial_in drivers/tty/serial/8250/8250.h:111 [inline]
>>  wait_for_xmitr+0x93/0x1e0 drivers/tty/serial/8250/8250_port.c:2033
>>  serial8250_console_putchar+0x1f/0x60
>> drivers/tty/serial/8250/8250_port.c:3170
>>  uart_console_write+0xac/0xe0 drivers/tty/serial/serial_core.c:1858
>>  serial8250_console_write+0x647/0xa20
>> drivers/tty/serial/8250/8250_port.c:3236
>>  univ8250_console_write+0x5f/0x70 drivers/tty/serial/8250/8250_core.c:590
>>  call_console_drivers kernel/printk/printk.c:1574 [inline]
>>  console_unlock+0x788/0xd70 kernel/printk/printk.c:2233
>>  vprintk_emit+0x4ad/0x590 kernel/printk/printk.c:1757
>>  vprintk_default+0x28/0x30 kernel/printk/printk.c:1796
>>  vprintk_func+0x57/0xc0 kernel/printk/printk_safe.c:379
>>  printk+0xaa/0xca kernel/printk/printk.c:1829
>>  __dev_set_promiscuity+0x2a4/0x630 net/core/dev.c:6609
>>  __dev_change_flags+0x559/0x990 net/core/dev.c:6826
>>  dev_change_flags+0x88/0x140 net/core/dev.c:6886
>>  dev_ifsioc+0x60d/0x9b0 net/core/dev_ioctl.c:257
>>  dev_ioctl+0x2c2/0xf90 net/core/dev_ioctl.c:566
>>  sock_do_ioctl+0x94/0xb0 net/socket.c:971
>>  sock_ioctl+0x2c2/0x440 net/socket.c:1061
>>  vfs_ioctl fs/ioctl.c:46 [inline]
>>  do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:686
>>  SYSC_ioctl fs/ioctl.c:701 [inline]
>>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
>>  entry_SYSCALL_64_fastpath+0x1f/0x96
>> RIP: 0033:0x452a39
>> RSP: 002b:00007f1ef8facc58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
>> RAX: ffffffffffffffda RBX: 00007f1ef8fad700 RCX: 0000000000452a39
>> RDX: 00000000208a3fe0 RSI: 0000000000008914 RDI: 0000000000000019
>> RBP: 0000000000a6f880 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000212 R12: 0000000000000000
>> R13: 0000000000a6f7ff R14: 00007f1ef8fad9c0 R15: 0000000000000002
>> Code: 24 d9 00 00 00 49 8d 7c 24 40 48 b8 00 00 00 00 00 fc ff df 48 89 fa
>> 48 c1 ea 03 d3 e3 80 3c 02 00 75 17 41 03 5c 24 40 89 da ec <5b> 0f b6 c0 41
>> 5c 5d c3 e8 88 ad 18 ff eb c2 e8 e1 ad 18 ff eb
> 
> 
> This looks like +rtnetlink issue.

Perhaps related to / fixed by: http://patchwork.ozlabs.org/patch/850957/

Re: INFO: task hung in cleanup_net

[Dmitry Vyukov]

On Tue, Dec 19, 2017 at 7:17 PM, David Ahern <dsahern@gmail.com> wrote:
> On 12/19/17 5:47 AM, Dmitry Vyukov wrote:
>> On Tue, Dec 19, 2017 at 1:33 PM, syzbot
>> <bot+b17f10c8a8c693b40723d40d6553fbc54d197679@syzkaller.appspotmail.com>
>> wrote:
>>> Hello,
>>>
>>> syzkaller hit the following crash on
>>> e40fd8d6b4d9f59b160faa1736f78fc07533ff37
>>> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
>>> compiler: gcc (GCC) 7.1.1 20170620
>>> .config is attached
>>> Raw console output is attached.
>>>
>>> Unfortunately, I don't have any reproducer for this bug yet.
>>>
>>>
>>> sctp: sctp_transport_update_pmtu: Reported pmtu 508 too low, using default
>>> minimum of 512
>>> sctp: sctp_transport_update_pmtu: Reported pmtu 508 too low, using default
>>> minimum of 512
>>> sctp: sctp_transport_update_pmtu: Reported pmtu 508 too low, using default
>>> minimum of 512
>>> INFO: task kworker/u4:11:3785 blocked for more than 120 seconds.
>>>       Not tainted 4.15.0-rc2-next-20171207+ #61
>>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>>> kworker/u4:11   D16448  3785      2 0x80000000
>>> Workqueue: netns cleanup_net
>>> Call Trace:
>>>  context_switch kernel/sched/core.c:2800 [inline]
>>>  __schedule+0x8eb/0x2060 kernel/sched/core.c:3376
>>>  schedule+0xf5/0x430 kernel/sched/core.c:3435
>>>  schedule_preempt_disabled+0x10/0x20 kernel/sched/core.c:3493
>>>  __mutex_lock_common kernel/locking/mutex.c:833 [inline]
>>>  __mutex_lock+0xaad/0x1a80 kernel/locking/mutex.c:893
>>>  mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
>>>  rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74
>>>  cleanup_net+0x24c/0xb60 net/core/net_namespace.c:453
>>>  process_one_work+0xbfd/0x1bc0 kernel/workqueue.c:2113
>>>  worker_thread+0x223/0x1990 kernel/workqueue.c:2247
>>>  kthread+0x37a/0x440 kernel/kthread.c:238
>>>  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:524
>>>
>>> Showing all locks held in the system:
>>> 2 locks held by khungtaskd/672:
>>>  #0:  (rcu_read_lock){....}, at: [<00000000b9bef8ab>]
>>> check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
>>>  #0:  (rcu_read_lock){....}, at: [<00000000b9bef8ab>] watchdog+0x1c5/0xd60
>>> kernel/hung_task.c:249
>>>  #1:  (tasklist_lock){.+.+}, at: [<000000006d6acf8b>]
>>> debug_show_all_locks+0xd3/0x400 kernel/locking/lockdep.c:4554
>>> 1 lock held by rsyslogd/2970:
>>>  #0:  (&f->f_pos_lock){+.+.}, at: [<000000001cede688>]
>>> __fdget_pos+0x131/0x1a0 fs/file.c:765
>>> 2 locks held by getty/3052:
>>>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
>>> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>>>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
>>> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
>>> 2 locks held by getty/3053:
>>>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
>>> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>>>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
>>> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
>>> 2 locks held by getty/3054:
>>>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
>>> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>>>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
>>> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
>>> 2 locks held by getty/3055:
>>>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
>>> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>>>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
>>> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
>>> 2 locks held by getty/3056:
>>>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
>>> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>>>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
>>> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
>>> 2 locks held by getty/3057:
>>>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
>>> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>>>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
>>> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
>>> 2 locks held by getty/3058:
>>>  #0:  (&tty->ldisc_sem){++++}, at: [<000000004e0245ba>]
>>> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>>>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ff863b18>]
>>> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
>>> 1 lock held by syz-executor2/3320:
>>>  #0:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
>>> net/core/rtnetlink.c:74
>>> 4 locks held by kworker/u4:11/3785:
>>>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
>>> __write_once_size include/linux/compiler.h:212 [inline]
>>>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
>>> atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
>>>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
>>> atomic_long_set include/asm-generic/atomic-long.h:57 [inline]
>>>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
>>> set_work_data kernel/workqueue.c:619 [inline]
>>>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
>>> set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline]
>>>  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<0000000087d81703>]
>>> process_one_work+0xad4/0x1bc0 kernel/workqueue.c:2084
>>>  #1:  (net_cleanup_work){+.+.}, at: [<000000008a817b5c>]
>>> process_one_work+0xb2f/0x1bc0 kernel/workqueue.c:2088
>>>  #2:  (net_mutex){+.+.}, at: [<0000000079150fd8>] cleanup_net+0x247/0xb60
>>> net/core/net_namespace.c:450
>>>  #3:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
>>> net/core/rtnetlink.c:74
>>> 3 locks held by kworker/0:6/14978:
>>>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
>>> __write_once_size include/linux/compiler.h:212 [inline]
>>>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
>>> atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
>>>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
>>> atomic_long_set include/asm-generic/atomic-long.h:57 [inline]
>>>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
>>> set_work_data kernel/workqueue.c:619 [inline]
>>>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
>>> set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline]
>>>  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: [<0000000087d81703>]
>>> process_one_work+0xad4/0x1bc0 kernel/workqueue.c:2084
>>>  #1:  ((addr_chk_work).work){+.+.}, at: [<000000008a817b5c>]
>>> process_one_work+0xb2f/0x1bc0 kernel/workqueue.c:2088
>>>  #2:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
>>> net/core/rtnetlink.c:74
>>> 1 lock held by syz-executor2/15852:
>>>  #0:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
>>> net/core/rtnetlink.c:74
>>> 1 lock held by syz-executor7/15958:
>>>  #0:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
>>> net/core/rtnetlink.c:74
>>> 1 lock held by syz-executor7/15961:
>>>  #0:  (rtnl_mutex){+.+.}, at: [<0000000063c47ced>] rtnl_lock+0x17/0x20
>>> net/core/rtnetlink.c:74
>>>
>>> =============================================
>>>
>>> NMI backtrace for cpu 1
>>> CPU: 1 PID: 672 Comm: khungtaskd Not tainted 4.15.0-rc2-next-20171207+ #61
>>> 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+0x194/0x257 lib/dump_stack.c:53
>>>  nmi_cpu_backtrace+0x1d2/0x210 lib/nmi_backtrace.c:103
>>>  nmi_trigger_cpumask_backtrace+0x122/0x180 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+0x90c/0xd60 kernel/hung_task.c:249
>>>  kthread+0x37a/0x440 kernel/kthread.c:238
>>>  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:524
>>> Sending NMI from CPU 1 to CPUs 0:
>>> NMI backtrace for cpu 0
>>> CPU: 0 PID: 15938 Comm: syz-executor7 Not tainted 4.15.0-rc2-next-20171207+
>>> #61
>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>>> Google 01/01/2011
>>> RIP: 0010:inb arch/x86/include/asm/io.h:348 [inline]
>>> RIP: 0010:io_serial_in+0x6b/0x90 drivers/tty/serial/8250/8250_port.c:434
>>> RSP: 0018:ffff8801c1c173e8 EFLAGS: 00000002
>>> RAX: dffffc0000000000 RBX: 00000000000003fd RCX: 0000000000000000
>>> RDX: 00000000000003fd RSI: ffffc90001c88000 RDI: ffffffff880fa9c0
>>> RBP: ffff8801c1c173f8 R08: 0000000000000002 R09: 000000000000000c
>>> R10: 0000000000000000 R11: ffffffff87896d20 R12: ffffffff880fa980
>>> R13: 0000000000000020 R14: fffffbfff101f577 R15: fffffbfff101f53a
>>> FS:  00007f1ef8fad700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> CR2: 00007fbea91b6000 CR3: 00000001d0aaa000 CR4: 00000000001406f0
>>> DR0: 0000000020001000 DR1: 0000000020001000 DR2: 0000000020001020
>>> DR3: 0000000020000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
>>> Call Trace:
>>>  serial_in drivers/tty/serial/8250/8250.h:111 [inline]
>>>  wait_for_xmitr+0x93/0x1e0 drivers/tty/serial/8250/8250_port.c:2033
>>>  serial8250_console_putchar+0x1f/0x60
>>> drivers/tty/serial/8250/8250_port.c:3170
>>>  uart_console_write+0xac/0xe0 drivers/tty/serial/serial_core.c:1858
>>>  serial8250_console_write+0x647/0xa20
>>> drivers/tty/serial/8250/8250_port.c:3236
>>>  univ8250_console_write+0x5f/0x70 drivers/tty/serial/8250/8250_core.c:590
>>>  call_console_drivers kernel/printk/printk.c:1574 [inline]
>>>  console_unlock+0x788/0xd70 kernel/printk/printk.c:2233
>>>  vprintk_emit+0x4ad/0x590 kernel/printk/printk.c:1757
>>>  vprintk_default+0x28/0x30 kernel/printk/printk.c:1796
>>>  vprintk_func+0x57/0xc0 kernel/printk/printk_safe.c:379
>>>  printk+0xaa/0xca kernel/printk/printk.c:1829
>>>  __dev_set_promiscuity+0x2a4/0x630 net/core/dev.c:6609
>>>  __dev_change_flags+0x559/0x990 net/core/dev.c:6826
>>>  dev_change_flags+0x88/0x140 net/core/dev.c:6886
>>>  dev_ifsioc+0x60d/0x9b0 net/core/dev_ioctl.c:257
>>>  dev_ioctl+0x2c2/0xf90 net/core/dev_ioctl.c:566
>>>  sock_do_ioctl+0x94/0xb0 net/socket.c:971
>>>  sock_ioctl+0x2c2/0x440 net/socket.c:1061
>>>  vfs_ioctl fs/ioctl.c:46 [inline]
>>>  do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:686
>>>  SYSC_ioctl fs/ioctl.c:701 [inline]
>>>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
>>>  entry_SYSCALL_64_fastpath+0x1f/0x96
>>> RIP: 0033:0x452a39
>>> RSP: 002b:00007f1ef8facc58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
>>> RAX: ffffffffffffffda RBX: 00007f1ef8fad700 RCX: 0000000000452a39
>>> RDX: 00000000208a3fe0 RSI: 0000000000008914 RDI: 0000000000000019
>>> RBP: 0000000000a6f880 R08: 0000000000000000 R09: 0000000000000000
>>> R10: 0000000000000000 R11: 0000000000000212 R12: 0000000000000000
>>> R13: 0000000000a6f7ff R14: 00007f1ef8fad9c0 R15: 0000000000000002
>>> Code: 24 d9 00 00 00 49 8d 7c 24 40 48 b8 00 00 00 00 00 fc ff df 48 89 fa
>>> 48 c1 ea 03 d3 e3 80 3c 02 00 75 17 41 03 5c 24 40 89 da ec <5b> 0f b6 c0 41
>>> 5c 5d c3 e8 88 ad 18 ff eb c2 e8 e1 ad 18 ff eb
>>
>>
>> This looks like +rtnetlink issue.
>
> Perhaps related to / fixed by: http://patchwork.ozlabs.org/patch/850957/

If you think so, let's tell syzbot about it:

#syz fix: net: Fix double free and memory corruption in get_net_ns_by_id()