INFO: task kworker/u4:4:29348 blocked for more than 140 seconds.
      Not tainted 4.9.146+ #84
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:4    D25688 29348      2 0x80000000
Workqueue: writeback wb_workfn (flush-7:0)
 ffff8801975a97c0 0000000000000000 ffff8801d2052680 ffffffff8302d180
 ffff8801db621018 ffff88019b2e6fd0 ffffffff8280a0f2 0000000000000296
 0000000000000002 0000000041b58ab3 00ffffff82e2af2a ffff8801db6218f0
Call Trace:
 [<ffffffff8280b61f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3553
 [<ffffffff81ad52b2>] blk_queue_enter+0x462/0x560 block/blk-core.c:664
 [<ffffffff81ad5750>] generic_make_request+0x1b0/0x800 block/blk-core.c:2046
 [<ffffffff81ad5e50>] submit_bio+0xb0/0x410 block/blk-core.c:2123
 [<ffffffff815bf449>] submit_bh_wbc.isra.17+0x3a9/0x590 fs/buffer.c:3101
 [<ffffffff815bfa7d>] __block_write_full_page+0x44d/0x810 fs/buffer.c:1789
 [<ffffffff815c033e>] block_write_full_page+0x23e/0x2a0 fs/buffer.c:2977
 [<ffffffff815c7374>] blkdev_writepage+0x24/0x30 fs/block_dev.c:312
 [<ffffffff8142ef64>] __writepage+0x64/0xc0 mm/page-writeback.c:2293
 [<ffffffff8142d995>] write_cache_pages+0x4d5/0xe80 mm/page-writeback.c:2231
 [<ffffffff814329ca>] generic_writepages+0xda/0x150 mm/page-writeback.c:2317
 [<ffffffff815c731d>] blkdev_writepages+0x1d/0x30 fs/block_dev.c:1764
 [<ffffffff814340ef>] do_writepages+0xef/0x1d0 mm/page-writeback.c:2331
 [<ffffffff8159f2f9>] __writeback_single_inode+0xd9/0x1020 fs/fs-writeback.c:1320
 [<ffffffff815a06ec>] writeback_sb_inodes+0x4ac/0xe70 fs/fs-writeback.c:1584
 [<ffffffff815a11ab>] __writeback_inodes_wb+0xfb/0x1e0 fs/fs-writeback.c:1653
 [<ffffffff815a17a2>] wb_writeback+0x512/0xbd0 fs/fs-writeback.c:1762
 [<ffffffff815a4f1c>] wb_check_old_data_flush fs/fs-writeback.c:1877 [inline]
 [<ffffffff815a4f1c>] wb_do_writeback fs/fs-writeback.c:1901 [inline]
 [<ffffffff815a4f1c>] wb_workfn+0x8bc/0xe90 fs/fs-writeback.c:1930
 [<ffffffff81131091>] process_one_work+0x831/0x15f0 kernel/workqueue.c:2092
 [<ffffffff81131f26>] worker_thread+0xd6/0x1140 kernel/workqueue.c:2226
 [<ffffffff81142ccd>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff8281a55c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373

Showing all locks held in the system:
2 locks held by khungtaskd/24:
 #0:  (rcu_read_lock){......}, at: [<ffffffff8131c22c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8131c22c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff813feb1f>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/2030:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff82818482>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff81d38032>] n_tty_read+0x202/0x1830 drivers/tty/n_tty.c:2156
3 locks held by kworker/u4:4/29348:
 #0:  ("writeback"){.+.+.+}, at: [<ffffffff81130f9c>] process_one_work+0x73c/0x15f0 kernel/workqueue.c:2085
 #1:  ((&(&wb->dwork)->work)){+.+.+.}, at: [<ffffffff81130fd4>] process_one_work+0x774/0x15f0 kernel/workqueue.c:2089
 #2:  (&type->s_umount_key#22){.+.+..}, at: [<ffffffff81514bd0>] trylock_super+0x20/0xf0 fs/super.c:393
3 locks held by syz-executor2/31247:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff81de824c>] lo_ioctl+0x8c/0x1910 drivers/block/loop.c:1372
 #1:  (lock#2){+.+...}, at: [<ffffffff8143f32a>] lru_add_drain_all+0x4a/0x400 mm/swap.c:695
 #2:  (cpu_hotplug.dep_map){++++++}, at: [<ffffffff810e1b02>] get_online_cpus+0x32/0x90 kernel/cpu.c:253
1 lock held by syz-executor2/31362:
 #0:  (&type->s_umount_key#32){++++++}, at: [<ffffffff815b2a16>] SYSC_syncfs fs/sync.c:164 [inline]
 #0:  (&type->s_umount_key#32){++++++}, at: [<ffffffff815b2a16>] SyS_syncfs+0x86/0xe0 fs/sync.c:154

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

NMI backtrace for cpu 0
CPU: 0 PID: 24 Comm: khungtaskd Not tainted 4.9.146+ #84
 ffff8801d9907d08 ffffffff81b43aa9 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff81098440 ffff8801d9907d40
 ffffffff81b4ebb9 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81b43aa9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81b43aa9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81b4ebb9>] nmi_cpu_backtrace.cold.0+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81b4eb4c>] nmi_trigger_cpumask_backtrace+0x12c/0x151 lib/nmi_backtrace.c:60
 [<ffffffff81098544>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff8131c7bd>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff8131c7bd>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff8131c7bd>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff8131c7bd>] watchdog+0x6ad/0xa20 kernel/hung_task.c:239
 [<ffffffff81142ccd>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff8281a55c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 31242 Comm: syz-executor1 Not tainted 4.9.146+ #84
task: ffff88019b7baf80 task.stack: ffff8801a6798000
RIP: 0033:[<0000000000401654>] 
c [<0000000000401654>] 0x401654
RSP: 002b:00007f49e765b710  EFLAGS: 00000282
RAX: 00000000cec2db1f RBX: 000000000000000b RCX: 0000000000457669
RDX: 0000000000000000 RSI: 00007f49e765b740 RDI: 000000000000000b
RBP: 0000000000000000 R08: 0000000000000000 R09: 00000000004bdbbd
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS:  00007f49e765c700(0000) GS:ffff8801db700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2fb23000 CR3: 00000001c5460000 CR4: 00000000001606b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400