Date:   Wed, 14 Feb 2018 05:59:02 -0800
From:   syzbot <syzbot+a3926c3116d237751fd8@...kaller.appspotmail.com>
To:     christian.brauner@...ntu.com, daniel@...earbox.net,
        davem@...emloft.net, dsahern@...il.com, fw@...len.de,
        jakub.kicinski@...ronome.com, 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 linkwatch_event

Hello,

syzbot hit the following crash on upstream commit
a2e5790d841658485d642196dbb0927303d6c22f (Wed Feb 7 06:15:42 2018 +0000)
Merge branch 'akpm' (patches from Andrew)

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+a3926c3116d237751fd8@...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 kworker/1:3:1828 blocked for more than 120 seconds.
       Not tainted 4.15.0+ #301
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/1:3     D19968  1828      2 0x80000000
Workqueue: events linkwatch_event
Call Trace:
  context_switch kernel/sched/core.c:2857 [inline]
  __schedule+0x8e2/0x2040 kernel/sched/core.c:3435
  schedule+0xf5/0x430 kernel/sched/core.c:3494
  schedule_preempt_disabled+0x10/0x20 kernel/sched/core.c:3552
  __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
  linkwatch_event+0x57/0xc0 net/core/link_watch.c:236
  process_one_work+0xbbf/0x1af0 kernel/workqueue.c:2113
  worker_thread+0x223/0x1990 kernel/workqueue.c:2247
  kthread+0x33c/0x400 kernel/kthread.c:238
  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:429

Showing all locks held in the system:
3 locks held by kworker/1:1/23:
  #0:  ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at:  
[<000000003027d709>] process_one_work+0xaaf/0x1af0 kernel/workqueue.c:2084
  #1:  ((addr_chk_work).work){+.+.}, at: [<00000000f19350a7>]  
process_one_work+0xb01/0x1af0 kernel/workqueue.c:2088
  #2:  (rtnl_mutex){+.+.}, at: [<0000000055e4e532>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74
2 locks held by khungtaskd/760:
  #0:  (rcu_read_lock){....}, at: [<000000007d511abd>]  
check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
  #0:  (rcu_read_lock){....}, at: [<000000007d511abd>] watchdog+0x1c5/0xd60  
kernel/hung_task.c:249
  #1:  (tasklist_lock){.+.+}, at: [<0000000078b2aec7>]  
debug_show_all_locks+0xd3/0x3d0 kernel/locking/lockdep.c:4470
3 locks held by kworker/1:3/1828:
  #0:  ((wq_completion)"events"){+.+.}, at: [<000000003027d709>]  
process_one_work+0xaaf/0x1af0 kernel/workqueue.c:2084
  #1:  ((linkwatch_work).work){+.+.}, at: [<00000000f19350a7>]  
process_one_work+0xb01/0x1af0 kernel/workqueue.c:2088
  #2:  (rtnl_mutex){+.+.}, at: [<0000000055e4e532>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74
1 lock held by rsyslogd/3879:
  #0:  (&f->f_pos_lock){+.+.}, at: [<000000001e0f1a09>]  
__fdget_pos+0x12b/0x190 fs/file.c:765
2 locks held by getty/4002:
  #0:  (&tty->ldisc_sem){++++}, at: [<000000004b23cd0c>]  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000007b8990ce>]  
n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
2 locks held by getty/4003:
  #0:  (&tty->ldisc_sem){++++}, at: [<000000004b23cd0c>]  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000007b8990ce>]  
n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
2 locks held by getty/4004:
  #0:  (&tty->ldisc_sem){++++}, at: [<000000004b23cd0c>]  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000007b8990ce>]  
n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
2 locks held by getty/4005:
  #0:  (&tty->ldisc_sem){++++}, at: [<000000004b23cd0c>]  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000007b8990ce>]  
n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
2 locks held by getty/4006:
  #0:  (&tty->ldisc_sem){++++}, at: [<000000004b23cd0c>]  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000007b8990ce>]  
n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
2 locks held by getty/4007:
  #0:  (&tty->ldisc_sem){++++}, at: [<000000004b23cd0c>]  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000007b8990ce>]  
n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
2 locks held by getty/22206:
  #0:  (&tty->ldisc_sem){++++}, at: [<000000004b23cd0c>]  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000007b8990ce>]  
n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
1 lock held by syz-executor0/953:
  #0:  (sk_lock-AF_INET6){+.+.}, at: [<00000000918a22c0>] lock_sock  
include/net/sock.h:1463 [inline]
  #0:  (sk_lock-AF_INET6){+.+.}, at: [<00000000918a22c0>]  
ipv6_getsockopt+0x1c5/0x2e0 net/ipv6/ipv6_sockglue.c:1370
1 lock held by syz-executor0/964:
  #0:  (sk_lock-AF_INET6){+.+.}, at: [<00000000918a22c0>] lock_sock  
include/net/sock.h:1463 [inline]
  #0:  (sk_lock-AF_INET6){+.+.}, at: [<00000000918a22c0>]  
ipv6_getsockopt+0x1c5/0x2e0 net/ipv6/ipv6_sockglue.c:1370
1 lock held by syz-executor0/970:
  #0:  (rtnl_mutex){+.+.}, at: [<0000000055e4e532>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74
1 lock held by syz-executor1/977:
  #0:  (rtnl_mutex){+.+.}, at: [<0000000055e4e532>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74
1 lock held by syz-executor1/987:
  #0:  (rtnl_mutex){+.+.}, at: [<0000000055e4e532>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74
1 lock held by syz-executor1/1007:
  #0:  (rtnl_mutex){+.+.}, at: [<0000000055e4e532>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74
1 lock held by syz-executor1/1008:
  #0:  (rtnl_mutex){+.+.}, at: [<0000000055e4e532>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74
1 lock held by syz-executor3/986:
  #0:  (rtnl_mutex){+.+.}, at: [<0000000055e4e532>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74
1 lock held by syz-executor3/1009:
  #0:  (rtnl_mutex){+.+.}, at: [<0000000055e4e532>] rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:74

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

NMI backtrace for cpu 1
CPU: 1 PID: 760 Comm: khungtaskd Not tainted 4.15.0+ #301
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:429
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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