Date:   Fri, 16 Feb 2018 00:23:01 -0800
From:   syzbot <syzbot+06cc4590ce78d7611ef8@...kaller.appspotmail.com>
To:     christian.brauner@...ntu.com, daniel@...earbox.net,
        davem@...emloft.net, dsahern@...il.com, fw@...len.de,
        jbenc@...hat.com, linux-kernel@...r.kernel.org,
        lucien.xin@...il.com, mschiffer@...verse-factory.net,
        netdev@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        vyasevich@...il.com
Subject: INFO: task hung in tun_chr_close

Hello,

syzbot hit the following crash on upstream commit
1388c80438e69fc01d83fbe98da3cac24c3c8731 (Thu Feb 15 17:28:47 2018 +0000)
Merge branch 'sched-urgent-for-linus' of  
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+06cc4590ce78d7611ef8@...kaller.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.

INFO: task syz-executor3:4212 blocked for more than 120 seconds.
       Not tainted 4.16.0-rc1+ #314
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor3   D19392  4212      1 0x80000006
Call Trace:
  context_switch kernel/sched/core.c:2862 [inline]
  __schedule+0x905/0x2070 kernel/sched/core.c:3440
  schedule+0xf5/0x430 kernel/sched/core.c:3499
  schedule_preempt_disabled+0x10/0x20 kernel/sched/core.c:3557
  __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
  tun_detach drivers/net/tun.c:745 [inline]
  tun_chr_close+0x37/0x60 drivers/net/tun.c:3179
  __fput+0x327/0x7e0 fs/file_table.c:209
  ____fput+0x15/0x20 fs/file_table.c:243
  task_work_run+0x199/0x270 kernel/task_work.c:113
  exit_task_work include/linux/task_work.h:22 [inline]
  do_exit+0x9bb/0x1ad0 kernel/exit.c:865
  do_group_exit+0x149/0x400 kernel/exit.c:968
  get_signal+0x73a/0x16d0 kernel/signal.c:2469
  do_signal+0x90/0x1e90 arch/x86/kernel/signal.c:809
  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+0x6e5/0x940 arch/x86/entry/common.c:292
  entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x40dd9a
RSP: 002b:0000000000a2ed68 EFLAGS: 00000246 ORIG_RAX: 000000000000003d
RAX: fffffffffffffe00 RBX: 0000000000000051 RCX: 000000000040dd9a
RDX: 0000000040000000 RSI: 0000000000a2ed94 RDI: ffffffffffffffff
RBP: 0000000000a2eda0 R08: 0000000000000001 R09: 0000000002625940
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000a2f420
R13: 0000000000000195 R14: 0000000000000000 R15: 0000000002625914

Showing all locks held in the system:
2 locks held by khungtaskd/756:
  #0:  (rcu_read_lock){....}, at: [<000000006b36ceac>]  
check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
  #0:  (rcu_read_lock){....}, at: [<000000006b36ceac>] watchdog+0x1c5/0xd60  
kernel/hung_task.c:249
  #1:  (tasklist_lock){.+.+}, at: [<000000005abe57a4>]  
debug_show_all_locks+0xd3/0x3d0 kernel/locking/lockdep.c:4470
2 locks held by getty/4132:
  #0:  (&tty->ldisc_sem){++++}, at: [<00000000595260b7>]  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000c36b84df>]  
n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
2 locks held by getty/4133:
  #0:  (&tty->ldisc_sem){++++}, at: [<00000000595260b7>]  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000c36b84df>]  
n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
2 locks held by getty/4134:
  #0:  (&tty->ldisc_sem){++++}, at: [<00000000595260b7>]  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000c36b84df>]  
n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
2 locks held by getty/4135:
  #0:  (&tty->ldisc_sem){++++}, at: [<00000000595260b7>]  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000c36b84df>]  
n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
2 locks held by getty/4136:
  #0:  (&tty->ldisc_sem){++++}, at: [<00000000595260b7>]  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000c36b84df>]  
n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
2 locks held by getty/4137:
  #0:  (&tty->ldisc_sem){++++}, at: [<00000000595260b7>]  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000c36b84df>]  
n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
2 locks held by getty/4138:
  #0:  (&tty->ldisc_sem){++++}, at: [<00000000595260b7>]  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000c36b84df>]  
n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
1 lock held by syz-executor3/4212:
  #0:  (rtnl_mutex){+.+.}, at: [<00000000a8309eae>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74
3 locks held by kworker/0:2/4726:
  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at:  
[<00000000302cad21>] process_one_work+0xaaf/0x1af0 kernel/workqueue.c:2084
  #1:  ((addr_chk_work).work){+.+.}, at: [<0000000095b7c7c2>]  
process_one_work+0xb01/0x1af0 kernel/workqueue.c:2088
  #2:  (rtnl_mutex){+.+.}, at: [<00000000a8309eae>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74
3 locks held by kworker/0:3/7235:
  #0:  ((wq_completion)"events_power_efficient"){+.+.}, at:  
[<00000000302cad21>] process_one_work+0xaaf/0x1af0 kernel/workqueue.c:2084
  #1:  ((reg_check_chans).work){+.+.}, at: [<0000000095b7c7c2>]  
process_one_work+0xb01/0x1af0 kernel/workqueue.c:2088
  #2:  (rtnl_mutex){+.+.}, at: [<00000000a8309eae>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74
1 lock held by syz-executor6/7622:
  #0:  (sk_lock-AF_INET6){+.+.}, at: [<000000002f175fa6>] lock_sock  
include/net/sock.h:1463 [inline]
  #0:  (sk_lock-AF_INET6){+.+.}, at: [<000000002f175fa6>]  
ipv6_getsockopt+0x1c5/0x2e0 net/ipv6/ipv6_sockglue.c:1370
1 lock held by syz-executor6/7641:
  #0:  (rtnl_mutex){+.+.}, at: [<00000000a8309eae>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74
1 lock held by syz-executor6/7667:
  #0:  (sk_lock-AF_INET6){+.+.}, at: [<000000002f175fa6>] lock_sock  
include/net/sock.h:1463 [inline]
  #0:  (sk_lock-AF_INET6){+.+.}, at: [<000000002f175fa6>]  
ipv6_getsockopt+0x1c5/0x2e0 net/ipv6/ipv6_sockglue.c:1370
1 lock held by syz-executor6/7673:
  #0:  (rtnl_mutex){+.+.}, at: [<00000000a8309eae>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74
1 lock held by syz-executor3/7643:
  #0:  (rtnl_mutex){+.+.}, at: [<00000000a8309eae>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74
1 lock held by syz-executor2/7648:
  #0:  (rtnl_mutex){+.+.}, at: [<00000000a8309eae>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74
1 lock held by syz-executor2/7670:
  #0:  (rtnl_mutex){+.+.}, at: [<00000000a8309eae>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74

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

NMI backtrace for cpu 1
CPU: 1 PID: 756 Comm: khungtaskd Not tainted 4.16.0-rc1+ #314
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+0x33c/0x400 kernel/kthread.c:238
  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:407
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0x6/0x10  
arch/x86/include/asm/irqflags.h:54


---
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