syzbot

INFO: task syz-executor039:7883 blocked for more than 143 seconds.
      Not tainted 5.4.0-rc4+ #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor039 D27984  7883   7880 0x00004004
Call Trace:
 context_switch kernel/sched/core.c:3384 [inline]
 __schedule+0x74b/0xb80 kernel/sched/core.c:4069
 schedule+0x131/0x1e0 kernel/sched/core.c:4136
 schedule_timeout+0x46/0x240 kernel/time/timer.c:1871
 do_wait_for_common+0x2e7/0x4d0 kernel/sched/completion.c:83
 __wait_for_common kernel/sched/completion.c:104 [inline]
 wait_for_common kernel/sched/completion.c:115 [inline]
 wait_for_completion+0x47/0x60 kernel/sched/completion.c:136
 flush_workqueue+0x60d/0x14b0 kernel/workqueue.c:2826
 nbd_start_device_ioctl drivers/block/nbd.c:1272 [inline]
 __nbd_ioctl drivers/block/nbd.c:1347 [inline]
 nbd_ioctl+0x9d2/0xac0 drivers/block/nbd.c:1387
 __blkdev_driver_ioctl block/ioctl.c:304 [inline]
 blkdev_ioctl+0x807/0x2980 block/ioctl.c:606
 block_ioctl+0xbd/0x100 fs/block_dev.c:1954
 do_vfs_ioctl+0x744/0x1730 fs/ioctl.c:46
 ksys_ioctl fs/ioctl.c:713 [inline]
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0xe3/0x120 fs/ioctl.c:718
 do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4496e9
Code: 00 61 64 64 69 6e 67 20 61 20 72 75 6c 65 73 65 74 2d 73 70 65 63 69 66 69 63 20 22 6d 61 69 6e 22 20 71 75 65 75 65 00 00 70 <72> 6f 63 65 73 73 42 61 74 63 68 3a 20 62 61 74 63 68 20 6f 66 20
RSP: 002b:00007fd715da2ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dac48 RCX: 00000000004496e9
RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000005
RBP: 00000000006dac40 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dac4c
R13: 00007ffd73e6239f R14: 00007fd715da39c0 R15: 20c49ba5e353f7cf

Showing all locks held in the system:
1 lock held by khungtaskd/1070:
 #0: ffffffff888d3f80 (rcu_read_lock){....}, at: rcu_lock_acquire+0x4/0x30 include/linux/rcupdate.h:207
2 locks held by kworker/u5:0/1527:
 #0: ffff88809fa37d28 ((wq_completion)knbd0-recv){+.+.}, at: spin_unlock_irq include/linux/spinlock.h:388 [inline]
 #0: ffff88809fa37d28 ((wq_completion)knbd0-recv){+.+.}, at: process_one_work+0x75d/0x10e0 kernel/workqueue.c:2242
 #1: ffff8880a637fd78 ((work_completion)(&args->work)){+.+.}, at: process_one_work+0x79f/0x10e0 kernel/workqueue.c:2244
1 lock held by rsyslogd/7770:
 #0: ffff8880a04f7420 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x243/0x2e0 fs/file.c:801
2 locks held by getty/7860:
 #0: ffff88809b3bd090 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
 #1: ffffc90005f352e0 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x221/0x1b00 drivers/tty/n_tty.c:2156
2 locks held by getty/7861:
 #0: ffff888090daf090 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
 #1: ffffc90005f212e0 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x221/0x1b00 drivers/tty/n_tty.c:2156
2 locks held by getty/7862:
 #0: ffff8880a3a20090 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
 #1: ffffc90005f392e0 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x221/0x1b00 drivers/tty/n_tty.c:2156
2 locks held by getty/7863:
 #0: ffff8880a7bcc090 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
 #1: ffffc90005f152e0 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x221/0x1b00 drivers/tty/n_tty.c:2156
2 locks held by getty/7864:
 #0: ffff8880a35b0090 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
 #1: ffffc90005f192e0 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x221/0x1b00 drivers/tty/n_tty.c:2156
2 locks held by getty/7865:
 #0: ffff8880a2541090 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
 #1: ffffc90005f2d2e0 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x221/0x1b00 drivers/tty/n_tty.c:2156
2 locks held by getty/7866:
 #0: ffff88809b0f8090 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
 #1: ffffc90005f012e0 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x221/0x1b00 drivers/tty/n_tty.c:2156

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

NMI backtrace for cpu 1
CPU: 1 PID: 1070 Comm: khungtaskd Not tainted 5.4.0-rc4+ #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+0x1d8/0x2f8 lib/dump_stack.c:113
 nmi_cpu_backtrace+0xaf/0x1a0 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x174/0x290 lib/nmi_backtrace.c:62
 arch_trigger_cpumask_backtrace+0x10/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 trigger_all_cpu_backtrace+0x17/0x20 include/linux/nmi.h:146
 check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
 watchdog+0xbb9/0xbd0 kernel/hung_task.c:289
 kthread+0x332/0x350 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0xe/0x10 arch/x86/include/asm/irqflags.h:60