syzbot

INFO: task syzkaller681645:4295 blocked for more than 120 seconds.
      Not tainted 4.16.0-rc7+ #3
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syzkaller681645 D20744  4295   4293 0x00000000
Call Trace:
 context_switch kernel/sched/core.c:2862 [inline]
 __schedule+0x8fb/0x1ec0 kernel/sched/core.c:3440
 schedule+0xf5/0x430 kernel/sched/core.c:3499
 schedule_timeout+0x1a3/0x230 kernel/time/timer.c:1777
 do_wait_for_common kernel/sched/completion.c:86 [inline]
 __wait_for_common kernel/sched/completion.c:107 [inline]
 wait_for_common kernel/sched/completion.c:118 [inline]
 wait_for_completion+0x415/0x770 kernel/sched/completion.c:139
 ucma_destroy_id+0x2f0/0x500 drivers/infiniband/core/ucma.c:611
 ucma_write+0x2d6/0x3d0 drivers/infiniband/core/ucma.c:1649
 __vfs_write+0xef/0x970 fs/read_write.c:480
 vfs_write+0x189/0x510 fs/read_write.c:544
 SYSC_write fs/read_write.c:589 [inline]
 SyS_write+0xef/0x220 fs/read_write.c:581
 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x440719
RSP: 002b:00007ffc7e451f28 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007ffc7e451f50 RCX: 0000000000440719
RDX: 0000000000000018 RSI: 0000000020000080 RDI: 0000000000000003
RBP: 0000000000000000 R08: 00007ffc7e451fa0 R09: 00007ffc7e451fa0
R10: 00007ffc7e451fa0 R11: 0000000000000246 R12: 0000000000402040
R13: 00000000004020d0 R14: 0000000000000000 R15: 0000000000000000

Showing all locks held in the system:
2 locks held by khungtaskd/868:
 #0:  (rcu_read_lock){....}, at: [<00000000dbcbeec6>] check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
 #0:  (rcu_read_lock){....}, at: [<00000000dbcbeec6>] watchdog+0x1c5/0xd60 kernel/hung_task.c:249
 #1:  (tasklist_lock){.+.+}, at: [<000000003f35a062>] debug_show_all_locks+0xd3/0x3d0 kernel/locking/lockdep.c:4470
1 lock held by rsyslogd/4176:
 #0:  (&f->f_pos_lock){+.+.}, at: [<00000000337d089e>] __fdget_pos+0x12b/0x190 fs/file.c:765
2 locks held by getty/4266:
 #0:  (&tty->ldisc_sem){++++}, at: [<0000000091eb7f81>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000c6c6bab6>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4267:
 #0:  (&tty->ldisc_sem){++++}, at: [<0000000091eb7f81>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000c6c6bab6>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4268:
 #0:  (&tty->ldisc_sem){++++}, at: [<0000000091eb7f81>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000c6c6bab6>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4269:
 #0:  (&tty->ldisc_sem){++++}, at: [<0000000091eb7f81>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000c6c6bab6>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4270:
 #0:  (&tty->ldisc_sem){++++}, at: [<0000000091eb7f81>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000c6c6bab6>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4271:
 #0:  (&tty->ldisc_sem){++++}, at: [<0000000091eb7f81>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000c6c6bab6>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4272:
 #0:  (&tty->ldisc_sem){++++}, at: [<0000000091eb7f81>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000c6c6bab6>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131

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

NMI backtrace for cpu 0
CPU: 0 PID: 868 Comm: khungtaskd Not tainted 4.16.0-rc7+ #3
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+0x194/0x24d lib/dump_stack.c:53
 nmi_cpu_backtrace+0x1d2/0x210 lib/nmi_backtrace.c:103
 nmi_trigger_cpumask_backtrace+0x123/0x180 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+0x90c/0xd60 kernel/hung_task.c:249
 kthread+0x33c/0x400 kernel/kthread.c:238
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:406
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