INFO: task loop0:773 blocked for more than 120 seconds. Not tainted 4.15.0-rc8+ #271 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. loop0 D22336 773 2 0x80000000 Call Trace: context_switch kernel/sched/core.c:2799 [inline] __schedule+0x8eb/0x2060 kernel/sched/core.c:3375 schedule+0xf5/0x430 kernel/sched/core.c:3434 schedule_timeout+0x1a3/0x230 kernel/time/timer.c:1769 io_schedule_timeout+0x26/0x80 kernel/sched/core.c:5030 do_wait_for_common kernel/sched/completion.c:86 [inline] __wait_for_common kernel/sched/completion.c:107 [inline] wait_for_common_io kernel/sched/completion.c:124 [inline] wait_for_completion_io+0x415/0x770 kernel/sched/completion.c:172 submit_bio_wait+0x13f/0x1e0 block/bio.c:947 blkdev_issue_flush+0x226/0x310 block/blk-flush.c:548 blkdev_fsync+0x86/0xb0 fs/block_dev.c:632 vfs_fsync_range+0x110/0x260 fs/sync.c:196 vfs_fsync+0x29/0x30 fs/sync.c:210 lo_req_flush drivers/block/loop.c:444 [inline] do_req_filebacked drivers/block/loop.c:572 [inline] loop_handle_cmd drivers/block/loop.c:1724 [inline] loop_queue_work+0x12a2/0x3900 drivers/block/loop.c:1738 kthread_worker_fn+0x32b/0x980 kernel/kthread.c:642 loop_kthread_worker_fn+0x51/0x60 drivers/block/loop.c:841 kthread+0x33c/0x400 kernel/kthread.c:238 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:541 Showing all locks held in the system: 2 locks held by khungtaskd/746: #0: (rcu_read_lock){....}, at: [<00000000efd3275e>] check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline] #0: (rcu_read_lock){....}, at: [<00000000efd3275e>] watchdog+0x1c5/0xd60 kernel/hung_task.c:249 #1: (tasklist_lock){.+.+}, at: [<00000000afea723a>] debug_show_all_locks+0xd3/0x400 kernel/locking/lockdep.c:4464 2 locks held by getty/3627: #0: (&tty->ldisc_sem){++++}, at: [<00000000947c9e56>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: (&ldata->atomic_read_lock){+.+.}, at: [<00000000bf7c150e>] n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131 2 locks held by getty/3628: #0: (&tty->ldisc_sem){++++}, at: [<00000000947c9e56>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: (&ldata->atomic_read_lock){+.+.}, at: [<00000000bf7c150e>] n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131 2 locks held by getty/3629: #0: (&tty->ldisc_sem){++++}, at: [<00000000947c9e56>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: (&ldata->atomic_read_lock){+.+.}, at: [<00000000bf7c150e>] n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131 2 locks held by getty/3630: #0: (&tty->ldisc_sem){++++}, at: [<00000000947c9e56>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: (&ldata->atomic_read_lock){+.+.}, at: [<00000000bf7c150e>] n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131 2 locks held by getty/3631: #0: (&tty->ldisc_sem){++++}, at: [<00000000947c9e56>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: (&ldata->atomic_read_lock){+.+.}, at: [<00000000bf7c150e>] n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131 2 locks held by getty/3632: #0: (&tty->ldisc_sem){++++}, at: [<00000000947c9e56>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: (&ldata->atomic_read_lock){+.+.}, at: [<00000000bf7c150e>] n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131 2 locks held by getty/3633: #0: (&tty->ldisc_sem){++++}, at: [<00000000947c9e56>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: (&ldata->atomic_read_lock){+.+.}, at: [<00000000bf7c150e>] n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131 1 lock held by syz-executor7/5341: #0: (&lo->lo_ctl_mutex/1){+.+.}, at: [<00000000375dc342>] lo_ioctl+0x8b/0x1b70 drivers/block/loop.c:1355 ============================================= NMI backtrace for cpu 0 CPU: 0 PID: 746 Comm: khungtaskd Not tainted 4.15.0-rc8+ #271 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+0x194/0x257 lib/dump_stack.c:53 nmi_cpu_backtrace+0x1d2/0x210 lib/nmi_backtrace.c:103 nmi_trigger_cpumask_backtrace+0x122/0x180 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:541 Sending NMI from CPU 0 to CPUs 1: NMI backtrace for cpu 1 CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.15.0-rc8+ #271 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:__lock_acquire+0xa1a/0x3e00 kernel/locking/lockdep.c:3305 RSP: 0018:ffff8801d9f777b0 EFLAGS: 00000006 RAX: dffffc0000000000 RBX: 0000000000000001 RCX: 0000000000000002 RDX: 1ffffffff0fe11f9 RSI: 0000000000000000 RDI: ffffffff868c8c60 RBP: ffff8801d9f77b40 R08: ffffffff8163dceb R09: 0000000000000001 R10: 0000000000000000 R11: ffffffff87f08fc8 R12: 0000000000000000 R13: 0000000000000001 R14: 0000000000000002 R15: ffff8801d9f66300 FS: 0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fa1d35fddb8 CR3: 0000000006822003 CR4: 00000000001606e0 Call Trace: lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3914 seqcount_lockdep_reader_access include/linux/seqlock.h:81 [inline] read_seqcount_begin include/linux/seqlock.h:164 [inline] ktime_get+0x12f/0x3a0 kernel/time/timekeeping.c:762 tick_nohz_idle_exit+0x19b/0x690 kernel/time/tick-sched.c:1068 do_idle+0x10a/0x3b0 kernel/sched/idle.c:258 cpu_startup_entry+0x104/0x120 kernel/sched/idle.c:351 start_secondary+0x40a/0x590 arch/x86/kernel/smpboot.c:268 secondary_startup_64+0xa5/0xb0 arch/x86/kernel/head_64.S:237 Code: 5e 41 5f 5d 49 8d 62 f8 c3 4c 89 da 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 80 3c 02 00 0f 85 0a 33 00 00 49 81 3b e0 2c 33 87 <41> bd 00 00 00 00 44 0f 45 eb 83 fe 01 0f 87 85 f7 ff ff 89 f3