INFO: task hung in ip_mc_drop_socket

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
16e205cf42da1f497b10a4a24f563e6c0d574eec (Fri Apr 13 03:56:10 2018 +0000)
Merge tag 'drm-fixes-for-v4.17-rc1' of
git://people.freedesktop.org/~airlied/linux
syzbot dashboard link:
https://syzkaller.appspot.com/bug?extid=b1cd477797b530b62c45

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:
https://syzkaller.appspot.com/x/log.txt?id=5805692438970368
Kernel config:
https://syzkaller.appspot.com/x/.config?id=-5947642240294114534
compiler: gcc (GCC) 8.0.1 20180301 (experimental)
CC: [christia...@ubuntu.com da...@davemloft.net dsa...@gmail.com
f...@strlen.de jb...@redhat.com ktk...@virtuozzo.com
linux-...@vger.kernel.org lucie...@gmail.com net...@vger.kernel.org]

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+b1cd47...@syzkaller.appspotmail.com
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audit: type=1326 audit(1523607024.536:20979): auid=4294967295 uid=0 gid=0
ses=4294967295 pid=27806 comm="syz-executor2" exe="/root/syz-executor2"
sig=0 arch=c000003e syscall=202 compat=0 ip=0x455319 code=0x50000
IPVS: stopping backup sync thread 20377 ...
INFO: task ipvs-b:7:0:20377 blocked for more than 120 seconds.
Not tainted 4.16.0+ #2
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
ipvs-b:7:0 D26424 20377 2 0x80000000
Call Trace:
context_switch kernel/sched/core.c:2848 [inline]
__schedule+0x801/0x1e30 kernel/sched/core.c:3490
schedule+0xef/0x430 kernel/sched/core.c:3549
schedule_preempt_disabled+0x10/0x20 kernel/sched/core.c:3607
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0xe38/0x17f0 kernel/locking/mutex.c:893
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74
ip_mc_drop_socket+0x8f/0x270 net/ipv4/igmp.c:2643
inet_release+0x4e/0x1f0 net/ipv4/af_inet.c:413
sock_release+0x96/0x1b0 net/socket.c:594
sync_thread_backup+0x63a/0x698 net/netfilter/ipvs/ip_vs_sync.c:1770
kthread+0x345/0x410 kernel/kthread.c:238
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:411

Showing all locks held in the system:
3 locks held by kworker/1:1/24:
#0: 00000000656e2300 ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at:
__write_once_size include/linux/compiler.h:215 [inline]
#0: 00000000656e2300 ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at:
arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: 00000000656e2300 ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at:
atomic64_set include/asm-generic/atomic-instrumented.h:40 [inline]
#0: 00000000656e2300 ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at:
atomic_long_set include/asm-generic/atomic-long.h:57 [inline]
#0: 00000000656e2300 ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at:
set_work_data kernel/workqueue.c:617 [inline]
#0: 00000000656e2300 ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at:
set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
#0: 00000000656e2300 ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at:
process_one_work+0xaef/0x1b50 kernel/workqueue.c:2116
#1: 0000000017f5afeb ((addr_chk_work).work){+.+.}, at:
process_one_work+0xb46/0x1b50 kernel/workqueue.c:2120
#2: 00000000864ee988 (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20
net/core/rtnetlink.c:74
2 locks held by khungtaskd/890:
#0: 000000007e23833c (rcu_read_lock){....}, at:
check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
#0: 000000007e23833c (rcu_read_lock){....}, at: watchdog+0x1ff/0xf60
kernel/hung_task.c:249
#1: 0000000061d832b7 (tasklist_lock){.+.+}, at:
debug_show_all_locks+0xde/0x34a kernel/locking/lockdep.c:4470
2 locks held by getty/4497:
#0: 00000000655f8dae (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000c33c88a8 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4498:
#0: 0000000017e3b228 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000e9238b2b (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4499:
#0: 00000000171a5be8 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 0000000036e3babf (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4500:
#0: 00000000504bea56 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 000000006302d83f (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4501:
#0: 0000000038e6210b (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000d36be0a2 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4502:
#0: 00000000f28399a2 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000d716fb22 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4503:
#0: 000000009620c246 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 0000000043e965ff (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
1 lock held by ipvs-b:7:0/20377:
#0: 00000000864ee988 (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20
net/core/rtnetlink.c:74
2 locks held by syz-executor5/27811:
#0: 00000000864ee988 (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20
net/core/rtnetlink.c:74
#1: 00000000f5524889 (ipvs->sync_mutex){+.+.}, at:
do_ip_vs_set_ctl+0x562/0x1d30 net/netfilter/ipvs/ip_vs_ctl.c:2388
1 lock held by syz-executor5/27842:
#0: 00000000f5524889 (ipvs->sync_mutex){+.+.}, at:
do_ip_vs_set_ctl+0x339/0x1d30 net/netfilter/ipvs/ip_vs_ctl.c:2393
1 lock held by syz-executor5/27844:
#0: 00000000864ee988 (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20
net/core/rtnetlink.c:74
1 lock held by syz-executor5/27847:
#0: 00000000f5524889 (ipvs->sync_mutex){+.+.}, at:
do_ip_vs_set_ctl+0x339/0x1d30 net/netfilter/ipvs/ip_vs_ctl.c:2393
1 lock held by syz-executor5/27848:
#0: 00000000864ee988 (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20
net/core/rtnetlink.c:74
2 locks held by syz-executor5/27849:
#0: 0000000058d11033 (vlan_ioctl_mutex){+.+.}, at: sock_ioctl+0x3ab/0x680
net/socket.c:1057
#1: 00000000864ee988 (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20
net/core/rtnetlink.c:74
1 lock held by syz-executor5/27850:
#0: 00000000f5524889 (ipvs->sync_mutex){+.+.}, at:
do_ip_vs_set_ctl+0x339/0x1d30 net/netfilter/ipvs/ip_vs_ctl.c:2393
1 lock held by syz-executor5/27851:
#0: 00000000864ee988 (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20
net/core/rtnetlink.c:74
1 lock held by syz-executor5/27854:
#0: 00000000864ee988 (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20
net/core/rtnetlink.c:74
1 lock held by syz-executor0/27843:
#0: 00000000864ee988 (rtnl_mutex){+.+.}, at: rtnl_lock
net/core/rtnetlink.c:74 [inline]
#0: 00000000864ee988 (rtnl_mutex){+.+.}, at: rtnetlink_rcv_msg+0x40a/0xc10
net/core/rtnetlink.c:4643
1 lock held by syz-executor4/27834:
#0: 00000000864ee988 (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20
net/core/rtnetlink.c:74
1 lock held by syz-executor4/27853:
#0: 00000000864ee988 (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20
net/core/rtnetlink.c:74

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

NMI backtrace for cpu 0
CPU: 0 PID: 890 Comm: khungtaskd Not tainted 4.16.0+ #2
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1b9/0x294 lib/dump_stack.c:113
nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103
nmi_trigger_cpumask_backtrace+0x151/0x192 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+0xc10/0xf60 kernel/hung_task.c:249
kthread+0x345/0x410 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+ #2
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:mark_irqflags kernel/locking/lockdep.c:3011 [inline]
RIP: 0010:__lock_acquire+0x606/0x5130 kernel/locking/lockdep.c:3388
RSP: 0018:ffff8801db1076d0 EFLAGS: 00000002
RAX: 000000000000000e RBX: 000000000000003a RCX: 0000000000000002
RDX: 0000000000000000 RSI: ffff8801d9ed8b78 RDI: ffff8801d9ed8b99
RBP: ffff8801db107a60 R08: 0000000000000001 R09: 0000000000000000
R10: ffff8801d9ed8b78 R11: ffff8801d9ed8340 R12: ffff8801d9ed8b9a
R13: 0000000000000000 R14: 000000000000000e R15: ffff8801d9ed8b64
FS: 0000000000000000(0000) GS:ffff8801db100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f05a5e1d000 CR3: 00000001c817c000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
seqcount_lockdep_reader_access include/linux/seqlock.h:81 [inline]
read_seqcount_begin include/linux/seqlock.h:164 [inline]
ktime_get+0x146/0x430 kernel/time/timekeeping.c:738
tick_nohz_irq_enter kernel/time/tick-sched.c:1237 [inline]
tick_irq_enter+0x83/0x390 kernel/time/tick-sched.c:1258
irq_enter+0xb6/0xd0 kernel/softirq.c:346
scheduler_ipi+0x39b/0xa30 kernel/sched/core.c:1768
smp_reschedule_interrupt+0xed/0x660 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:ffff8801d9ee7c38 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff02
RAX: dffffc0000000000 RBX: 1ffff1003b3dcf8a RCX: 0000000000000000
RDX: 1ffffffff11630f0 RSI: 0000000000000001 RDI: ffffffff88b18780
RBP: ffff8801d9ee7c38 R08: ffffed003b6246c3 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
R13: ffff8801d9ee7cf0 R14: ffffffff8958d520 R15: 0000000000000000
arch_safe_halt arch/x86/include/asm/paravirt.h:94 [inline]
default_idle+0xc2/0x440 arch/x86/kernel/process.c:354
arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:345
default_idle_call+0x6d/0x90 kernel/sched/idle.c:93
cpuidle_idle_call kernel/sched/idle.c:153 [inline]
do_idle+0x395/0x560 kernel/sched/idle.c:262
cpu_startup_entry+0x104/0x120 kernel/sched/idle.c:368
start_secondary+0x426/0x5b0 arch/x86/kernel/smpboot.c:267
secondary_startup_64+0xa5/0xb0 arch/x86/kernel/head_64.S:242
Code: e2 07 38 d0 7f 08 84 c0 0f 85 10 0e 00 00 41 0f b6 42 22 45 84 ed 0f
88 c0 00 00 00 41 8b 93 04 08 00 00 a8 03 0f 84 20 07 00 00 <85> d2 0f 85
a3 0f 00 00 48 b8 00 00 00 00 00 fc ff df 4c 89 fa


---
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[syzbot]

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