INFO: task hung in nbd

INFO: task hung in nbd_ioctl (2)
Status: fixed on 2020/10/21 11:01
Reported-by: syzbot+2955441f38a151da301f@syzkaller.appspotmail.com
Fix commit: 7241d653bcc1 tipc: fix shutdown() of connection oriented socket
First crash: 623d, last: 377d

Fix bisection: fixed by (bisect log) :
commit 7241d653bcc17eaf4ccb9994f360168d8bfea32d
Author: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Sat Sep 5 06:14:47 2020 +0000

tipc: fix shutdown() of connection oriented socket

similar bugs (6):
Kernel	Title	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
linux-4.14	INFO: task hung in nbd_ioctl	C		done	18	630d	704d	1/1	fixed on 2019/12/28 10:32
upstream	INFO: task hung in nbd_ioctl (2)				37	385d	438d	17/22	fixed on 2020/09/25 01:17
upstream	INFO: task hung in nbd_ioctl	C	done		71	682d	717d	14/22	fixed on 2019/11/06 12:39
linux-4.19	INFO: task hung in nbd_ioctl	C			53	22d	706d	0/1	upstream: reported C repro on 2019/10/12 13:11
upstream	INFO: task hung in nbd_ioctl (3)	C	done	unreliable	11	6d17h	354d	0/22	upstream: reported C repro on 2020/09/28 07:17
linux-4.14	INFO: task hung in nbd_ioctl (3)	C			7	4d18h	308d	0/1	upstream: reported C repro on 2020/11/13 07:37

Sample crash report:

block nbd2: shutting down sockets
block nbd5: shutting down sockets
block nbd3: shutting down sockets
block nbd4: shutting down sockets
block nbd0: shutting down sockets
INFO: task syz-executor099:7227 blocked for more than 140 seconds.
      Not tainted 4.14.161-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor099 D29008  7227   7223 0x00000004
Call Trace:
 context_switch kernel/sched/core.c:2808 [inline]
 __schedule+0x7b8/0x1cd0 kernel/sched/core.c:3384
 schedule+0x92/0x1c0 kernel/sched/core.c:3428
 schedule_timeout+0x93b/0xe10 kernel/time/timer.c:1723
 do_wait_for_common kernel/sched/completion.c:91 [inline]
 __wait_for_common kernel/sched/completion.c:112 [inline]
 wait_for_common kernel/sched/completion.c:123 [inline]
 wait_for_completion+0x27c/0x420 kernel/sched/completion.c:144
 flush_workqueue+0x3d1/0x1400 kernel/workqueue.c:2674
 nbd_start_device_ioctl drivers/block/nbd.c:1239 [inline]
 __nbd_ioctl drivers/block/nbd.c:1310 [inline]
 nbd_ioctl+0x545/0xb30 drivers/block/nbd.c:1350
 __blkdev_driver_ioctl block/ioctl.c:297 [inline]
 blkdev_ioctl+0x96b/0x1860 block/ioctl.c:594
 block_ioctl+0xde/0x120 fs/block_dev.c:1881
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x7ae/0x1060 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x44a719
RSP: 002b:00007f34a8646ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dbc48 RCX: 000000000044a719
RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000006
RBP: 00000000006dbc40 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc4c
R13: 00007fff3033079f R14: 00007f34a86479c0 R15: 0000000000000000
INFO: task syz-executor099:7228 blocked for more than 140 seconds.
      Not tainted 4.14.161-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor099 D28432  7228   7221 0x00000004
Call Trace:
 context_switch kernel/sched/core.c:2808 [inline]
 __schedule+0x7b8/0x1cd0 kernel/sched/core.c:3384
 schedule+0x92/0x1c0 kernel/sched/core.c:3428
 schedule_timeout+0x93b/0xe10 kernel/time/timer.c:1723
 do_wait_for_common kernel/sched/completion.c:91 [inline]
 __wait_for_common kernel/sched/completion.c:112 [inline]
 wait_for_common kernel/sched/completion.c:123 [inline]
 wait_for_completion+0x27c/0x420 kernel/sched/completion.c:144
 flush_workqueue+0x3d1/0x1400 kernel/workqueue.c:2674
 nbd_start_device_ioctl drivers/block/nbd.c:1239 [inline]
 __nbd_ioctl drivers/block/nbd.c:1310 [inline]
 nbd_ioctl+0x545/0xb30 drivers/block/nbd.c:1350
 __blkdev_driver_ioctl block/ioctl.c:297 [inline]
 blkdev_ioctl+0x96b/0x1860 block/ioctl.c:594
 block_ioctl+0xde/0x120 fs/block_dev.c:1881
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x7ae/0x1060 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x44a719
RSP: 002b:00007f34a8646ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dbc48 RCX: 000000000044a719
RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000006
RBP: 00000000006dbc40 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc4c
R13: 00007fff3033079f R14: 00007f34a86479c0 R15: 0000000000000000
INFO: task syz-executor099:7229 blocked for more than 140 seconds.
      Not tainted 4.14.161-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor099 D28016  7229   7219 0x00000004
Call Trace:
 context_switch kernel/sched/core.c:2808 [inline]
 __schedule+0x7b8/0x1cd0 kernel/sched/core.c:3384
 schedule+0x92/0x1c0 kernel/sched/core.c:3428
 schedule_timeout+0x93b/0xe10 kernel/time/timer.c:1723
 do_wait_for_common kernel/sched/completion.c:91 [inline]
 __wait_for_common kernel/sched/completion.c:112 [inline]
 wait_for_common kernel/sched/completion.c:123 [inline]
 wait_for_completion+0x27c/0x420 kernel/sched/completion.c:144
 flush_workqueue+0x3d1/0x1400 kernel/workqueue.c:2674
 nbd_start_device_ioctl drivers/block/nbd.c:1239 [inline]
 __nbd_ioctl drivers/block/nbd.c:1310 [inline]
 nbd_ioctl+0x545/0xb30 drivers/block/nbd.c:1350
 __blkdev_driver_ioctl block/ioctl.c:297 [inline]
 blkdev_ioctl+0x96b/0x1860 block/ioctl.c:594
 block_ioctl+0xde/0x120 fs/block_dev.c:1881
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x7ae/0x1060 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x44a719
RSP: 002b:00007f34a8646ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dbc48 RCX: 000000000044a719
RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000006
RBP: 00000000006dbc40 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc4c
R13: 00007fff3033079f R14: 00007f34a86479c0 R15: 0000000000000000
INFO: task syz-executor099:7235 blocked for more than 140 seconds.
      Not tainted 4.14.161-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor099 D29008  7235   7222 0x00000004
Call Trace:
 context_switch kernel/sched/core.c:2808 [inline]
 __schedule+0x7b8/0x1cd0 kernel/sched/core.c:3384
 schedule+0x92/0x1c0 kernel/sched/core.c:3428
 schedule_timeout+0x93b/0xe10 kernel/time/timer.c:1723
 do_wait_for_common kernel/sched/completion.c:91 [inline]
 __wait_for_common kernel/sched/completion.c:112 [inline]
 wait_for_common kernel/sched/completion.c:123 [inline]
 wait_for_completion+0x27c/0x420 kernel/sched/completion.c:144
 flush_workqueue+0x3d1/0x1400 kernel/workqueue.c:2674
 nbd_start_device_ioctl drivers/block/nbd.c:1239 [inline]
 __nbd_ioctl drivers/block/nbd.c:1310 [inline]
 nbd_ioctl+0x545/0xb30 drivers/block/nbd.c:1350
 __blkdev_driver_ioctl block/ioctl.c:297 [inline]
 blkdev_ioctl+0x96b/0x1860 block/ioctl.c:594
 block_ioctl+0xde/0x120 fs/block_dev.c:1881
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x7ae/0x1060 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x44a719
RSP: 002b:00007f34a8646ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dbc48 RCX: 000000000044a719
RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000006
RBP: 00000000006dbc40 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc4c
R13: 00007fff3033079f R14: 00007f34a86479c0 R15: 0000000000000000
INFO: task syz-executor099:7236 blocked for more than 140 seconds.
      Not tainted 4.14.161-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor099 D28744  7236   7220 0x00000004
Call Trace:
 context_switch kernel/sched/core.c:2808 [inline]
 __schedule+0x7b8/0x1cd0 kernel/sched/core.c:3384
 schedule+0x92/0x1c0 kernel/sched/core.c:3428
 schedule_timeout+0x93b/0xe10 kernel/time/timer.c:1723
 do_wait_for_common kernel/sched/completion.c:91 [inline]
 __wait_for_common kernel/sched/completion.c:112 [inline]
 wait_for_common kernel/sched/completion.c:123 [inline]
 wait_for_completion+0x27c/0x420 kernel/sched/completion.c:144
 flush_workqueue+0x3d1/0x1400 kernel/workqueue.c:2674
 nbd_start_device_ioctl drivers/block/nbd.c:1239 [inline]
 __nbd_ioctl drivers/block/nbd.c:1310 [inline]
 nbd_ioctl+0x545/0xb30 drivers/block/nbd.c:1350
 __blkdev_driver_ioctl block/ioctl.c:297 [inline]
 blkdev_ioctl+0x96b/0x1860 block/ioctl.c:594
 block_ioctl+0xde/0x120 fs/block_dev.c:1881
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x7ae/0x1060 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x44a719
RSP: 002b:00007f34a8646ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dbc48 RCX: 000000000044a719
RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000006
RBP: 00000000006dbc40 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc4c
R13: 00007fff3033079f R14: 00007f34a86479c0 R15: 0000000000000000
INFO: task syz-executor099:7239 blocked for more than 140 seconds.
      Not tainted 4.14.161-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor099 D29008  7239   7218 0x00000004
Call Trace:
 context_switch kernel/sched/core.c:2808 [inline]
 __schedule+0x7b8/0x1cd0 kernel/sched/core.c:3384
 schedule+0x92/0x1c0 kernel/sched/core.c:3428
 schedule_timeout+0x93b/0xe10 kernel/time/timer.c:1723
 do_wait_for_common kernel/sched/completion.c:91 [inline]
 __wait_for_common kernel/sched/completion.c:112 [inline]
 wait_for_common kernel/sched/completion.c:123 [inline]
 wait_for_completion+0x27c/0x420 kernel/sched/completion.c:144
 flush_workqueue+0x3d1/0x1400 kernel/workqueue.c:2674
 nbd_start_device_ioctl drivers/block/nbd.c:1239 [inline]
 __nbd_ioctl drivers/block/nbd.c:1310 [inline]
 nbd_ioctl+0x545/0xb30 drivers/block/nbd.c:1350
 __blkdev_driver_ioctl block/ioctl.c:297 [inline]
 blkdev_ioctl+0x96b/0x1860 block/ioctl.c:594
 block_ioctl+0xde/0x120 fs/block_dev.c:1881
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x7ae/0x1060 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x44a719
RSP: 002b:00007f34a8646ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dbc48 RCX: 000000000044a719
RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000006
RBP: 00000000006dbc40 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc4c
R13: 00007fff3033079f R14: 00007f34a86479c0 R15: 0000000000000000

Showing all locks held in the system:
1 lock held by khungtaskd/1045:
 #0:  (tasklist_lock){.+.+}, at: [<ffffffff8148c8d8>] debug_show_all_locks+0x7f/0x21f kernel/locking/lockdep.c:4544
2 locks held by kworker/u5:0/1179:
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] work_static include/linux/workqueue.h:199 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] set_work_data kernel/workqueue.c:619 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] process_one_work+0x76e/0x1600 kernel/workqueue.c:2085
 #1:  ((&args->work)){+.+.}, at: [<ffffffff813d585b>] process_one_work+0x7ab/0x1600 kernel/workqueue.c:2089
1 lock held by rsyslogd/7070:
 #0:  (&f->f_pos_lock){+.+.}, at: [<ffffffff81966a5b>] __fdget_pos+0xab/0xd0 fs/file.c:769
2 locks held by getty/7193:
 #0:  (&tty->ldisc_sem){++++}, at: [<ffffffff86650bc3>] ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83492216>] n_tty_read+0x1e6/0x17d0 drivers/tty/n_tty.c:2156
2 locks held by getty/7194:
 #0:  (&tty->ldisc_sem){++++}, at: [<ffffffff86650bc3>] ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83492216>] n_tty_read+0x1e6/0x17d0 drivers/tty/n_tty.c:2156
2 locks held by getty/7195:
 #0:  (&tty->ldisc_sem){++++}, at: [<ffffffff86650bc3>] ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83492216>] n_tty_read+0x1e6/0x17d0 drivers/tty/n_tty.c:2156
2 locks held by getty/7196:
 #0:  (&tty->ldisc_sem){++++}, at: [<ffffffff86650bc3>] ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83492216>] n_tty_read+0x1e6/0x17d0 drivers/tty/n_tty.c:2156
2 locks held by getty/7197:
 #0:  (&tty->ldisc_sem){++++}, at: [<ffffffff86650bc3>] ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83492216>] n_tty_read+0x1e6/0x17d0 drivers/tty/n_tty.c:2156
2 locks held by getty/7198:
 #0:  (&tty->ldisc_sem){++++}, at: [<ffffffff86650bc3>] ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83492216>] n_tty_read+0x1e6/0x17d0 drivers/tty/n_tty.c:2156
2 locks held by getty/7199:
 #0:  (&tty->ldisc_sem){++++}, at: [<ffffffff86650bc3>] ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83492216>] n_tty_read+0x1e6/0x17d0 drivers/tty/n_tty.c:2156
2 locks held by kworker/u5:1/7246:
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] work_static include/linux/workqueue.h:199 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] set_work_data kernel/workqueue.c:619 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] process_one_work+0x76e/0x1600 kernel/workqueue.c:2085
 #1:  ((&args->work)){+.+.}, at: [<ffffffff813d585b>] process_one_work+0x7ab/0x1600 kernel/workqueue.c:2089
2 locks held by kworker/u5:2/7249:
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] work_static include/linux/workqueue.h:199 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] set_work_data kernel/workqueue.c:619 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] process_one_work+0x76e/0x1600 kernel/workqueue.c:2085
 #1:  ((&args->work)){+.+.}, at: [<ffffffff813d585b>] process_one_work+0x7ab/0x1600 kernel/workqueue.c:2089
2 locks held by kworker/u5:3/7250:
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] work_static include/linux/workqueue.h:199 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] set_work_data kernel/workqueue.c:619 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] process_one_work+0x76e/0x1600 kernel/workqueue.c:2085
 #1:  ((&args->work)){+.+.}, at: [<ffffffff813d585b>] process_one_work+0x7ab/0x1600 kernel/workqueue.c:2089
2 locks held by kworker/u5:4/7251:
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] work_static include/linux/workqueue.h:199 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] set_work_data kernel/workqueue.c:619 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] process_one_work+0x76e/0x1600 kernel/workqueue.c:2085
 #1:  ((&args->work)){+.+.}, at: [<ffffffff813d585b>] process_one_work+0x7ab/0x1600 kernel/workqueue.c:2089
2 locks held by kworker/u5:5/7252:
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] work_static include/linux/workqueue.h:199 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] set_work_data kernel/workqueue.c:619 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline]
 #0:  ("knbd%d-recv"nbd->index){+.+.}, at: [<ffffffff813d581e>] process_one_work+0x76e/0x1600 kernel/workqueue.c:2085
 #1:  ((&args->work)){+.+.}, at: [<ffffffff813d585b>] process_one_work+0x7ab/0x1600 kernel/workqueue.c:2089

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

NMI backtrace for cpu 0
CPU: 0 PID: 1045 Comm: khungtaskd Not tainted 4.14.161-syzkaller #0
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+0x142/0x197 lib/dump_stack.c:58
 nmi_cpu_backtrace.cold+0x57/0x94 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x141/0x189 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:140 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:195 [inline]
 watchdog+0x5e7/0xb90 kernel/hung_task.c:274
 kthread+0x319/0x430 kernel/kthread.c:232
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at pc 0xffffffff866516ae

Crashes (16):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro
ci2-linux-4-14	2020/01/03 17:07	linux-4.14.y	4c5bf01e16a7	9dcc1191	.config	log	report	syz	C
ci2-linux-4-14	2020/09/04 19:55	linux-4.14.y	2f166cdcf8a9	abf9ba4f	.config	log	report
ci2-linux-4-14	2020/08/30 11:06	linux-4.14.y	d7e78d08fa77	d5a3ae1f	.config	log	report
ci2-linux-4-14	2020/08/15 08:33	linux-4.14.y	14b58326976d	5ce13532	.config	log	report
ci2-linux-4-14	2020/07/05 14:46	linux-4.14.y	b850307b279c	22f87567	.config	log	report
ci2-linux-4-14	2020/06/28 06:45	linux-4.14.y	b850307b279c	a2cdad9d	.config	log	report
ci2-linux-4-14	2020/06/08 19:43	linux-4.14.y	c6db52a88798	7604bb03	.config	log	report
ci2-linux-4-14	2020/06/01 12:51	linux-4.14.y	4f68020fef1c	a0331e89	.config	log	report
ci2-linux-4-14	2020/04/24 10:45	linux-4.14.y	050272a0423e	03d97a1b	.config	log	report
ci2-linux-4-14	2020/04/19 15:44	linux-4.14.y	c10b57a567e4	6dfd45e1	.config	log	report
ci2-linux-4-14	2020/04/14 05:54	linux-4.14.y	c10b57a567e4	7c54686a	.config	log	report
ci2-linux-4-14	2020/03/31 09:46	linux-4.14.y	01364dad1d45	c8d1cc20	.config	log	report
ci2-linux-4-14	2020/03/28 04:45	linux-4.14.y	01364dad1d45	831e9a81	.config	log	report
ci2-linux-4-14	2020/03/16 23:32	linux-4.14.y	12cd844a39ed	749688d2	.config	log	report
ci2-linux-4-14	2020/03/14 19:39	linux-4.14.y	12cd844a39ed	749688d2	.config	log	report
ci2-linux-4-14	2020/02/01 15:09	linux-4.14.y	9fa690a2a016	326d4c78	.config	log	report