INFO: task hung in stop_sync_thread

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 38f41ec1 Merge 4.4.125 into android-4.4
git tree: android-4.4
console output: https://syzkaller.appspot.com/x/log.txt?x=14252667800000
kernel config: https://syzkaller.appspot.com/x/.config?x=d3227609e1874daa
dashboard link: https://syzkaller.appspot.com/bug?extid=7e1968aaf6aa3e9dd346
compiler: gcc (GCC) 7.1.1 20170620
userspace arch: i386
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17aa0c3b800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+7e1968...@syzkaller.appspotmail.com

IPVS: Creating netns size=2552 id=1
IPVS: sync thread started: state = BACKUP, mcast_ifn = lo, syncid = 0, id =
0
IPVS: stopping backup sync thread 3818 ...
INFO: task syz-executor0:3817 blocked for more than 120 seconds.
Not tainted 4.4.125-g38f41ec #21
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0 D ffff8801d9767790 27144 3817 3809 0x20020004
ffff8801d9767790 ffff8801d93c9800 ffff880100000000 1ffff1003b2eceec
ffff8801d93ca000 ffff8801db21fdb8 ffff8801db21fde0 ffff8801db21f4d8
ffff8801db21f4c0 ffff8800ada7b000 ffff8801d93c9800 0000000000000000
Call Trace:
[<ffffffff8376b82a>] schedule+0x7a/0x1b0 kernel/sched/core.c:3359
[<ffffffff83776b40>] schedule_timeout+0x3a0/0x970 kernel/time/timer.c:1515
[<ffffffff8376e919>] do_wait_for_common kernel/sched/completion.c:75
[inline]
[<ffffffff8376e919>] __wait_for_common kernel/sched/completion.c:93
[inline]
[<ffffffff8376e919>] wait_for_common kernel/sched/completion.c:101 [inline]
[<ffffffff8376e919>] wait_for_completion+0x209/0x2e0
kernel/sched/completion.c:122
[<ffffffff8119165e>] kthread_stop+0x12e/0x790 kernel/kthread.c:497
[<ffffffff830b5129>] stop_sync_thread+0x3d9/0x740
net/netfilter/ipvs/ip_vs_sync.c:1995
[<ffffffff8309e088>] do_ip_vs_set_ctl+0x228/0xba0
net/netfilter/ipvs/ip_vs_ctl.c:2362
[<ffffffff82f9d7da>] compat_nf_sockopt net/netfilter/nf_sockopt.c:145
[inline]
[<ffffffff82f9d7da>] compat_nf_setsockopt+0xfa/0x130
net/netfilter/nf_sockopt.c:155
[<ffffffff83104beb>] compat_ip_setsockopt+0x8b/0xd0
net/ipv4/ip_sockglue.c:1251
[<ffffffff8310ddc5>] inet_csk_compat_setsockopt+0x95/0x120
net/ipv4/inet_connection_sock.c:914
[<ffffffff831236dd>] compat_tcp_setsockopt+0x3d/0x70 net/ipv4/tcp.c:2652
[<ffffffff82df7d12>] compat_sock_common_setsockopt+0xb2/0x140
net/core/sock.c:2670
[<ffffffff82edfde9>] C_SYSC_setsockopt net/compat.c:384 [inline]
[<ffffffff82edfde9>] compat_SyS_setsockopt+0x149/0x290 net/compat.c:367
[<ffffffff81006d91>] do_syscall_32_irqs_on arch/x86/entry/common.c:392
[inline]
[<ffffffff81006d91>] do_fast_syscall_32+0x321/0x8a0
arch/x86/entry/common.c:459
[<ffffffff8377b2aa>] sysenter_flags_fixed+0xd/0x17
1 lock held by syz-executor0/3817:
#0: (ipvs->sync_mutex){+.+.+.}, at: [<ffffffff8309e079>]
do_ip_vs_set_ctl+0x219/0xba0 net/netfilter/ipvs/ip_vs_ctl.c:2361
Sending NMI to all CPUs:
NMI backtrace for cpu 0
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.125-g38f41ec #21
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
task: ffffffff84217840 task.stack: ffffffff84200000
RIP: 0010:[<ffffffff810d0666>] [<ffffffff810d0666>]
native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:49
RSP: 0018:ffffffff84207dc0 EFLAGS: 00000246
RAX: 0000000000000007 RBX: ffffffff847dec48 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffff8421811c
RBP: ffffffff84207dc0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: fffffbfff07088c0 R14: ffffffff847ecfb8 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fff05539628 CR3: 00000000b69f2000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
ffffffff84207df8 ffffffff81027e65 ffffffff84208000 ffffffff847dec48
fffffbfff07088c0 ffffffff847ecfb8 0000000000000000 ffffffff84207e08
ffffffff810293da ffffffff84207e20 ffffffff81221948 dffffc0000000000
Call Trace:
[<ffffffff81027e65>] arch_safe_halt arch/x86/include/asm/paravirt.h:117
[inline]
[<ffffffff81027e65>] default_idle+0x55/0x3c0 arch/x86/kernel/process.c:290
[<ffffffff810293da>] arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:281
[<ffffffff81221948>] default_idle_call+0x48/0x70 kernel/sched/idle.c:93
[<ffffffff8122204d>] cpuidle_idle_call kernel/sched/idle.c:157 [inline]
[<ffffffff8122204d>] cpu_idle_loop kernel/sched/idle.c:253 [inline]
[<ffffffff8122204d>] cpu_startup_entry+0x5fd/0x8f0 kernel/sched/idle.c:301
[<ffffffff837667b9>] rest_init+0x189/0x190 init/main.c:410
[<ffffffff84823811>] start_kernel+0x6b9/0x6ee init/main.c:682
[<ffffffff84822312>] x86_64_start_reservations+0x2a/0x2c
arch/x86/kernel/head64.c:196
[<ffffffff84822454>] x86_64_start_kernel+0x140/0x163
arch/x86/kernel/head64.c:185
Code: 00 00 00 00 00 55 48 89 e5 fa 5d c3 66 0f 1f 84 00 00 00 00 00 55 48
89 e5 fb 5d c3 66 0f 1f 84 00 00 00 00 00 55 48 89 e5 fb f4 <5d> c3 0f 1f
84 00 00 00 00 00 55 48 89 e5 f4 5d c3 66 0f 1f 84
NMI backtrace for cpu 1
CPU: 1 PID: 486 Comm: khungtaskd Not tainted 4.4.125-g38f41ec #21
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
task: ffff8800bacc4800 task.stack: ffff8800baca0000
RIP: 0010:[<ffffffff810c3f87>] [<ffffffff810c3f87>] native_apic_mem_write
arch/x86/include/asm/apic.h:94 [inline]
RIP: 0010:[<ffffffff810c3f87>] [<ffffffff810c3f87>]
__default_send_IPI_dest_field arch/x86/include/asm/ipi.h:119 [inline]
RIP: 0010:[<ffffffff810c3f87>] [<ffffffff810c3f87>] _flat_send_IPI_mask
arch/x86/kernel/apic/apic_flat_64.c:61 [inline]
RIP: 0010:[<ffffffff810c3f87>] [<ffffffff810c3f87>]
flat_send_IPI_mask+0xf7/0x1a0 arch/x86/kernel/apic/apic_flat_64.c:69
RSP: 0018:ffff8800baca7cb8 EFLAGS: 00000046
RAX: 0000000003000000 RBX: 0000000000000c00 RCX: 0000000000000000
RDX: 0000000000000c00 RSI: 0000000000000000 RDI: ffffffffff5fb300
RBP: ffff8800baca7ce0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000246
R13: 0000000000000003 R14: ffffffff8426f5a0 R15: 0000000000000002
FS: 0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f86a88fd3c0 CR3: 00000000b69f2000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
ffffffff8426f5a0 ffffffff847f0b40 fffffbfff08fdc1c dffffc0000000000
ffff8801db31bca0 ffff8800baca7d00 ffffffff810b9abb ffffffff839f6dc0
0000000000000003 ffff8800baca7d60 ffffffff81d11764 ffffffff8141b993
Call Trace:
[<ffffffff810b9abb>] nmi_raise_cpu_backtrace+0x5b/0x70
arch/x86/kernel/apic/hw_nmi.c:33
[<ffffffff81d11764>] nmi_trigger_all_cpu_backtrace+0x4a4/0x550
lib/nmi_backtrace.c:85
[<ffffffff810b9b54>] arch_trigger_all_cpu_backtrace+0x14/0x20
arch/x86/kernel/apic/hw_nmi.c:38
[<ffffffff813695ca>] trigger_all_cpu_backtrace include/linux/nmi.h:44
[inline]
[<ffffffff813695ca>] check_hung_task kernel/hung_task.c:125 [inline]
[<ffffffff813695ca>] check_hung_uninterruptible_tasks
kernel/hung_task.c:182 [inline]
[<ffffffff813695ca>] watchdog+0x6fa/0xae0 kernel/hung_task.c:238
[<ffffffff81190b48>] kthread+0x268/0x300 kernel/kthread.c:211
[<ffffffff83779d95>] ret_from_fork+0x55/0x80 arch/x86/entry/entry_64.S:510
Code: b3 5f ff f6 c4 10 75 e1 44 89 e8 c1 e0 18 89 04 25 10 b3 5f ff 44 89
fa 09 da 80 cf 04 41 83 ff 02 0f 44 d3 89 14 25 00 b3 5f ff <41> f7 c4 00
02 00 00 74 1a e8 2b 33 17 00 4c 89 e7 57 9d 0f 1f


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