[<ffffffff838b2b6e>] entry_SYSCALL_64_fastpath+0x29/0xe8
INFO: task syz-executor6:8308 blocked for more than 120 seconds.
      Not tainted 4.9.77-g033d019 #14
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor6   D29584  8308  11257 0x00000004
 ffff8801cbd16000 ffff8801c4386a00 ffff8801c9fc0540 ffff8801c1f69800
 ffff8801db321b98 ffff8801cd4efb00 ffffffff838a1adb 0000000041b58ab3
 ffffffff84193178 00ffffff8123bda0 ffff8801db322468 ffff8801db322490
Call Trace:
 [<ffffffff838a307f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3550
 [<ffffffff838af1dc>] schedule_timeout+0x56c/0x10b0 kernel/time/timer.c:1768
 [<ffffffff838a128e>] io_schedule_timeout+0x1be/0x390 kernel/sched/core.c:5172
 [<ffffffff838a49ee>] do_wait_for_common kernel/sched/completion.c:75 [inline]
 [<ffffffff838a49ee>] __wait_for_common kernel/sched/completion.c:93 [inline]
 [<ffffffff838a49ee>] wait_for_common_io kernel/sched/completion.c:107 [inline]
 [<ffffffff838a49ee>] wait_for_completion_io+0x20e/0x2e0 kernel/sched/completion.c:155
 [<ffffffff81cdaabb>] submit_bio_wait+0x11b/0x180 block/bio.c:885
 [<ffffffff81d0dc67>] blkdev_issue_flush+0x157/0x220 block/blk-flush.c:518
 [<ffffffff81629ed5>] blkdev_fsync+0x85/0xb0 fs/block_dev.c:378
 [<ffffffff8161583a>] vfs_fsync_range+0x10a/0x250 fs/sync.c:195
 [<ffffffff816159f2>] vfs_fsync fs/sync.c:209 [inline]
 [<ffffffff816159f2>] do_fsync+0x42/0xb0 fs/sync.c:219
 [<ffffffff81616199>] SYSC_fdatasync fs/sync.c:233 [inline]
 [<ffffffff81616199>] SyS_fdatasync+0x19/0x20 fs/sync.c:231
 [<ffffffff838b2b6e>] entry_SYSCALL_64_fastpath+0x29/0xe8

Showing all locks held in the system:
2 locks held by khungtaskd/514:
 #0:  (rcu_read_lock){......}, at: [<ffffffff81372d85>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff81372d85>] watchdog+0x125/0xa70 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81237f00>] debug_show_all_locks+0x70/0x280 kernel/locking/lockdep.c:4336
2 locks held by getty/3303:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838b0d52>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff82009514>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133

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

NMI backtrace for cpu 0
CPU: 0 PID: 514 Comm: khungtaskd Not tainted 4.9.77-g033d019 #14
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d855fd00 ffffffff81d941c9 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810babe0 ffff8801d855fd38
 ffffffff81d9f2ed 0000000000000000 0000000000000000 ffff8801bf00b418
Call Trace:
 [<ffffffff81d941c9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d941c9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81d9f2ed>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81d9f427>] nmi_trigger_cpumask_backtrace+0x117/0x190 lib/nmi_backtrace.c:60
 [<ffffffff810bacd4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81373350>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81373350>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81373350>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81373350>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff8119a6fd>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838b2ea9>] ret_from_fork+0x59/0x70 arch/x86/entry/entry_64.S:466
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.9.77-g033d019 #14
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801da3d3000 task.stack: ffff8801da3e8000
RIP: 0010:[<ffffffff811cb4a0>] 
c [<ffffffff811cb4a0>] sched_ttwu_pending+0x0/0x160 include/trace/events/sched.h:234
RSP: 0018:ffff8801db307fa0  EFLAGS: 00000002
RAX: 0000000000000007 RBX: 0000000000021b80 RCX: 1ffffffff083fe7d
RDX: 0000000000000000 RSI: ffffffff83c18780 RDI: ffff8801da3d387c
RBP: ffff8801db307fd0 R08: 0000000000000001 R09: ffff88021fffd048
R10: ffff88021fffd058 R11: ffff88021fffd050 R12: 0000000000021b80
R13: ffff8801db300000 R14: ffff8801da3d3000 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000096f188 CR3: 00000001c9dac000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff811cb8e2
c ffff8801da3d3000
c ffffffff841ff840
c 0000000000000001
c
 ffffffff84a36978
c 0000000000000000
c ffff8801db307fe8
c ffffffff838b73a6
c
 ffffffff84a27868
c ffff8801da3efd98
c ffffffff838b4fc0
c ffff8801da3efce8
c
Call Trace:
 [<ffffffff838b73a6>] __smp_reschedule_interrupt arch/x86/kernel/smp.c:259 [inline]
 [<ffffffff838b73a6>] smp_reschedule_interrupt+0x66/0x80 arch/x86/kernel/smp.c:266
 [<ffffffff838b4fc0>] reschedule_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:764
 <EOI> 
d [<ffffffff838b17c6>] ? native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:53
 [<ffffffff838b0df5>] arch_safe_halt arch/x86/include/asm/paravirt.h:103 [inline]
 [<ffffffff838b0df5>] default_idle+0x55/0x360 arch/x86/kernel/process.c:295
 [<ffffffff8106bc9a>] arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:286
 [<ffffffff838b1c06>] default_idle_call+0x36/0x60 kernel/sched/idle.c:97
 [<ffffffff81226500>] cpuidle_idle_call kernel/sched/idle.c:155 [inline]
 [<ffffffff81226500>] cpu_idle_loop kernel/sched/idle.c:248 [inline]
 [<ffffffff81226500>] cpu_startup_entry+0x2b0/0x380 kernel/sched/idle.c:303
 [<ffffffff810afc93>] start_secondary+0x303/0x3e0 arch/x86/kernel/smpboot.c:254
Code: 
cff 
c48 
c89 
c95 
cc8 
cfe 
cff 
cff 
c4c 
c89 
c95 
ce0 
cfe 
cff 
cff 
ce8 
c77 
c2d 
c37 
c00 
c48 
c8b 
c95 
cc8 
cfe 
cff 
cff 
c4c 
c8b 
c95 
ce0 
cfe 
cff 
cff 
ce9 
c15 
cfd 
cff 
cff 
c0f 
c1f 
c40 
c00 
c<55> 
c48 
c89 
ce5 
c41 
c57 
c41 
c56 
c41 
c55 
c41 
c54 
c53 
c48 
cc7 
cc3 
c80 
c1b 
c02 
c00 
c48 
c