INFO: task can't die in nbd_ioctl

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    de69ee6d Add linux-next specific files for 20200930
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=10d04f17900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4919771fba5919e5
dashboard link: https://syzkaller.appspot.com/bug?extid=69a90a5e8f6b59086b2a
compiler:       gcc (GCC) 10.1.0-syz 20200507

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+69a90a5e8f6b59086b2a@xxxxxxxxxxxxxxxxxxxxxxxxx

INFO: task syz-executor.0:4417 can't die for more than 143 seconds.
task:syz-executor.0  state:D stack:28472 pid: 4417 ppid:  6852 flags:0x10004004
Call Trace:
 context_switch kernel/sched/core.c:3777 [inline]
 __schedule+0xec5/0x2200 kernel/sched/core.c:4526
 schedule+0xcf/0x270 kernel/sched/core.c:4604
 schedule_timeout+0x1d8/0x250 kernel/time/timer.c:1855
 do_wait_for_common kernel/sched/completion.c:85 [inline]
 __wait_for_common kernel/sched/completion.c:106 [inline]
 wait_for_common kernel/sched/completion.c:117 [inline]
 wait_for_completion+0x163/0x260 kernel/sched/completion.c:138
 flush_workqueue+0x3ff/0x13e0 kernel/workqueue.c:2832
 nbd_start_device_ioctl drivers/block/nbd.c:1331 [inline]
 __nbd_ioctl drivers/block/nbd.c:1408 [inline]
 nbd_ioctl+0x76d/0xbe0 drivers/block/nbd.c:1448
 __blkdev_driver_ioctl block/ioctl.c:228 [inline]
 blkdev_ioctl+0x2a7/0x7f0 block/ioctl.c:623
 block_ioctl+0xf9/0x140 fs/block_dev.c:1866
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl fs/ioctl.c:739 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45dd99
Code: Bad RIP value.
RSP: 002b:00007f39f37eac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000012e80 RCX: 000000000045dd99
RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000004
RBP: 000000000118bf58 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118bf2c
R13: 00007fff8753a28f R14: 00007f39f37eb9c0 R15: 000000000118bf2c
INFO: task syz-executor.0:4417 blocked for more than 144 seconds.
      Not tainted 5.9.0-rc7-next-20200930-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor.0  state:D stack:28472 pid: 4417 ppid:  6852 flags:0x10004004
Call Trace:
 context_switch kernel/sched/core.c:3777 [inline]
 __schedule+0xec5/0x2200 kernel/sched/core.c:4526
 schedule+0xcf/0x270 kernel/sched/core.c:4604
 schedule_timeout+0x1d8/0x250 kernel/time/timer.c:1855
 do_wait_for_common kernel/sched/completion.c:85 [inline]
 __wait_for_common kernel/sched/completion.c:106 [inline]
 wait_for_common kernel/sched/completion.c:117 [inline]
 wait_for_completion+0x163/0x260 kernel/sched/completion.c:138
 flush_workqueue+0x3ff/0x13e0 kernel/workqueue.c:2832
 nbd_start_device_ioctl drivers/block/nbd.c:1331 [inline]
 __nbd_ioctl drivers/block/nbd.c:1408 [inline]
 nbd_ioctl+0x76d/0xbe0 drivers/block/nbd.c:1448
 __blkdev_driver_ioctl block/ioctl.c:228 [inline]
 blkdev_ioctl+0x2a7/0x7f0 block/ioctl.c:623
 block_ioctl+0xf9/0x140 fs/block_dev.c:1866
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl fs/ioctl.c:739 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45dd99
Code: Bad RIP value.
RSP: 002b:00007f39f37eac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000012e80 RCX: 000000000045dd99
RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000004
RBP: 000000000118bf58 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118bf2c
R13: 00007fff8753a28f R14: 00007f39f37eb9c0 R15: 000000000118bf2c

Showing all locks held in the system:
1 lock held by khungtaskd/1178:
 #0: ffffffff8a553d00 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:6221
1 lock held by in:imklog/6557:
 #0: ffff8880a0a526b0 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:930
2 locks held by kworker/u5:2/6867:
 #0: ffff888093c7f138 ((wq_completion)knbd0-recv){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff888093c7f138 ((wq_completion)knbd0-recv){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
 #0: ffff888093c7f138 ((wq_completion)knbd0-recv){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
 #0: ffff888093c7f138 ((wq_completion)knbd0-recv){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:616 [inline]
 #0: ffff888093c7f138 ((wq_completion)knbd0-recv){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
 #0: ffff888093c7f138 ((wq_completion)knbd0-recv){+.+.}-{0:0}, at: process_one_work+0x821/0x15a0 kernel/workqueue.c:2240
 #1: ffffc900017b7da8 ((work_completion)(&args->work)){+.+.}-{0:0}, at: process_one_work+0x854/0x15a0 kernel/workqueue.c:2244

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

NMI backtrace for cpu 0
CPU: 0 PID: 1178 Comm: khungtaskd Not tainted 5.9.0-rc7-next-20200930-syzkaller #0
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+0x198/0x1fb lib/dump_stack.c:118
 nmi_cpu_backtrace.cold+0x44/0xd7 lib/nmi_backtrace.c:105
 nmi_trigger_cpumask_backtrace+0x1b3/0x230 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:147 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:253 [inline]
 watchdog+0xd89/0xf30 kernel/hung_task.c:339
 kthread+0x3af/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 6835 Comm: syz-fuzzer Not tainted 5.9.0-rc7-next-20200930-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0033:0x415b7a
Code: 89 ac 24 c8 00 00 00 48 8d ac 24 c8 00 00 00 48 8b 94 24 e0 00 00 00 48 83 fa 08 0f 84 4d 09 00 00 48 8b 1d 98 4a 5a 01 84 03 <90> 48 8b b4 24 d8 00 00 00 48 bf 00 00 00 00 00 80 00 00 48 8d 04
RSP: 002b:000000c026e52b98 EFLAGS: 00000246
RAX: 000000c026e52c18 RBX: 00007f1f2ef8f000 RCX: 000000c000083980
RDX: 0000000000000030 RSI: 0000000000000000 RDI: 0000000000000030
RBP: 000000c026e52c60 R08: 00000000008f7880 R09: 0000000000203000
R10: 000000c011bb4cf0 R11: 0000000000000001 R12: ffffffffffffffff
R13: 0000000000000046 R14: 0000000000000045 R15: 00000000000000aa
FS:  0000000001992df0 GS:  0000000000000000


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