Hello,

syzbot hit the following crash on upstream commit
3fd14cdcc05a682b03743683ce3a726898b20555 (Fri Apr 6 19:15:41 2018 +0000)
Merge tag 'mtd/for-4.17' of git://git.infradead.org/linux-mtd
syzbot dashboard link: https://syzkaller.appspot.com/bug?extid=7810ed2e0cb359580c17


Unfortunately, I don't have any reproducer for this crash yet.
Raw console output: https://syzkaller.appspot.com/x/log.txt?id=5452586266132480 Kernel config: https://syzkaller.appspot.com/x/.config?id=-5813481738265533882
compiler: gcc (GCC) 8.0.1 20180301 (experimental)

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Reported-by: syzbot+7810ed2e0cb359580...@syzkaller.appspotmail.com
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IPVS: stopping backup sync thread 25820 ...
IPVS: sync thread started: state = BACKUP, mcast_ifn = lo, syncid = 0, id = 0 IPVS: sync thread started: state = BACKUP, mcast_ifn = bridge0, syncid = 5, id = 0
IPVS: stopping backup sync thread 25825 ...
INFO: task syz-executor4:25814 blocked for more than 120 seconds.
      Not tainted 4.16.0+ #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor4   D23496 25814   4577 0x00000004
Call Trace:
 context_switch kernel/sched/core.c:2848 [inline]
 __schedule+0x807/0x1e40 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
 do_ip_vs_set_ctl+0x562/0x1d30 net/netfilter/ipvs/ip_vs_ctl.c:2388
 nf_sockopt net/netfilter/nf_sockopt.c:106 [inline]
 nf_setsockopt+0x7d/0xd0 net/netfilter/nf_sockopt.c:115
 ip_setsockopt+0xd8/0xf0 net/ipv4/ip_sockglue.c:1253
 udp_setsockopt+0x62/0xa0 net/ipv4/udp.c:2413
 ipv6_setsockopt+0x149/0x170 net/ipv6/ipv6_sockglue.c:917
 udpv6_setsockopt+0x62/0xa0 net/ipv6/udp.c:1424
 sock_common_setsockopt+0x9a/0xe0 net/core/sock.c:3039
 __sys_setsockopt+0x1bd/0x390 net/socket.c:1903
 SYSC_setsockopt net/socket.c:1914 [inline]
 SyS_setsockopt+0x34/0x50 net/socket.c:1911
 do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x455259
RSP: 002b:00007f2f6a5c0c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007f2f6a5c16d4 RCX: 0000000000455259
RDX: 000000000000048b RSI: 0000000000000000 RDI: 0000000000000019
RBP: 000000000072bea0 R08: 0000000000000018 R09: 0000000000000000
R10: 0000000020000100 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000520 R14: 00000000006faba0 R15: 0000000000000000

Showing all locks held in the system:
3 locks held by kworker/1:0/18:
#0: 000000005979db97 ((wq_completion)"events"){+.+.}, at: __write_once_size include/linux/compiler.h:215 [inline] #0: 000000005979db97 ((wq_completion)"events"){+.+.}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline] #0: 000000005979db97 ((wq_completion)"events"){+.+.}, at: atomic64_set include/asm-generic/atomic-instrumented.h:40 [inline] #0: 000000005979db97 ((wq_completion)"events"){+.+.}, at: atomic_long_set include/asm-generic/atomic-long.h:57 [inline] #0: 000000005979db97 ((wq_completion)"events"){+.+.}, at: set_work_data kernel/workqueue.c:617 [inline] #0: 000000005979db97 ((wq_completion)"events"){+.+.}, at: set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline] #0: 000000005979db97 ((wq_completion)"events"){+.+.}, at: process_one_work+0xaef/0x1b50 kernel/workqueue.c:2116 #1: 0000000034433a79 (deferred_process_work){+.+.}, at: process_one_work+0xb46/0x1b50 kernel/workqueue.c:2120 #2: 00000000c152a7e0 (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74
3 locks held by kworker/1:1/25:
#0: 0000000004c9dcc7 ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: __write_once_size include/linux/compiler.h:215 [inline] #0: 0000000004c9dcc7 ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline] #0: 0000000004c9dcc7 ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: atomic64_set include/asm-generic/atomic-instrumented.h:40 [inline] #0: 0000000004c9dcc7 ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: atomic_long_set include/asm-generic/atomic-long.h:57 [inline] #0: 0000000004c9dcc7 ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: set_work_data kernel/workqueue.c:617 [inline] #0: 0000000004c9dcc7 ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline] #0: 0000000004c9dcc7 ((wq_completion)"%s"("ipv6_addrconf")){+.+.}, at: process_one_work+0xaef/0x1b50 kernel/workqueue.c:2116 #1: 00000000fcc18889 ((addr_chk_work).work){+.+.}, at: process_one_work+0xb46/0x1b50 kernel/workqueue.c:2120 #2: 00000000c152a7e0 (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74
2 locks held by khungtaskd/882:
#0: 000000009c9e6fd6 (rcu_read_lock){....}, at: check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline] #0: 000000009c9e6fd6 (rcu_read_lock){....}, at: watchdog+0x1ff/0xf60 kernel/hung_task.c:249 #1: 0000000086407811 (tasklist_lock){.+.+}, at: debug_show_all_locks+0xde/0x34a kernel/locking/lockdep.c:4470
2 locks held by getty/4501:
#0: 0000000055d02921 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: 000000008595151e (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4502:
#0: 00000000edb0964a (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: 00000000b6f18e79 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4503:
#0: 000000002383a0c1 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: 000000004c0469cb (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4504:
#0: 00000000f3591a78 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: 00000000148d6bd9 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4505:
#0: 000000007c3caa91 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: 00000000da492356 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4506:
#0: 000000006efbca4d (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: 0000000070306487 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/24388:
#0: 000000003730ef1a (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: 00000000de906401 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by syz-executor4/25814:
#0: 00000000c152a7e0 (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74 #1: 000000008674f843 (ipvs->sync_mutex){+.+.}, at: do_ip_vs_set_ctl+0x562/0x1d30 net/netfilter/ipvs/ip_vs_ctl.c:2388
1 lock held by syz-executor4/25826:
#0: 000000008674f843 (ipvs->sync_mutex){+.+.}, at: do_ip_vs_set_ctl+0x339/0x1d30 net/netfilter/ipvs/ip_vs_ctl.c:2393
1 lock held by syz-executor4/25834:
#0: 00000000c152a7e0 (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74
1 lock held by ipvs-b:3:0/25825:
#0: 00000000c152a7e0 (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74

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

NMI backtrace for cpu 0
CPU: 0 PID: 882 Comm: khungtaskd Not tainted 4.16.0+ #4
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 skipped: idling at native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:54


---
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