INFO: task syz-executor1:13970 blocked for more than 120 seconds.
      Not tainted 4.9.105-gd7e64f8 #40
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor1   D27184 13970   9175 0x00000004
 ffff8801da3a0000 ffff880183e94fc0 ffff880190b24fc0 ffff8801d79b3000
 ffff8801db221c18 ffff8801857f7b48 ffffffff839e8c1d ffff8801da3a08c8
 ffffed003b474118 ffff8801da3a0000 00fffc0000000000 ffff8801db2224e8
Call Trace:
 [<ffffffff839ea21f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839eaba3>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839ef026>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839ef026>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff825cd256>] loop_control_ioctl+0x186/0x300 drivers/block/loop.c:1920
 [<ffffffff815b2f5c>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b2f5c>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b2f5c>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b3fdf>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b3fdf>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f9b13>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Showing all locks held in the system:
2 locks held by khungtaskd/519:
 #0:  (rcu_read_lock){......}, at: [<ffffffff81366b9c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff81366b9c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81426180>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3775:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f7cc2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff82120062>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
2 locks held by syz-executor1/13970:
 #0:  (loop_index_mutex){+.+.+.}, at: [<ffffffff825cd14a>] loop_control_ioctl+0x7a/0x300 drivers/block/loop.c:1906
 #1:  (&lo->lo_ctl_mutex#2){+.+.+.}, at: [<ffffffff825cd256>] loop_control_ioctl+0x186/0x300 drivers/block/loop.c:1920
2 locks held by syz-executor2/13976:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825cab6b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
 #1:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff81e5682e>] blkdev_reread_part+0x1e/0x40 block/ioctl.c:189
1 lock held by syz-executor2/13997:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8163165c>] __blkdev_get+0x10c/0xd60 fs/block_dev.c:1268
1 lock held by syz-executor0/13988:
 #0:  (loop_index_mutex){+.+.+.}, at: [<ffffffff825cd444>] loop_probe+0x74/0x180 drivers/block/loop.c:1886
1 lock held by syz-executor0/13998:
 #0:  (loop_index_mutex){+.+.+.}, at: [<ffffffff825cd444>] loop_probe+0x74/0x180 drivers/block/loop.c:1886
2 locks held by blkid/13986:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8163165c>] __blkdev_get+0x10c/0xd60 fs/block_dev.c:1268
 #1:  (loop_index_mutex){+.+.+.}, at: [<ffffffff825c5c0b>] lo_open+0x1b/0xa0 drivers/block/loop.c:1555

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

NMI backtrace for cpu 1
CPU: 1 PID: 519 Comm: khungtaskd Not tainted 4.9.105-gd7e64f8 #40
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d84c7d08 ffffffff81eb41a9 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b96a0 ffff8801d84c7d40
 ffffffff81ebf4a7 0000000000000001 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb41a9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb41a9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebf4a7>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebf43a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b97a4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81367134>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81367134>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81367134>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81367134>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119d04d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f9cdc>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 1835 Comm: kworker/0:2 Not tainted 4.9.105-gd7e64f8 #40
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_power_efficient gc_worker
c
task: ffff8801cee0b000 task.stack: ffff8801ce0b0000
RIP: 0010:[<ffffffff81ed1492>] 
c [<ffffffff81ed1492>] strlen+0x62/0xa0 lib/string.c:481
RSP: 0018:ffff8801ce0b79d8  EFLAGS: 00000046
RAX: ffffffff8411aff3 RBX: dffffc0000000000 RCX: 0000000000000003
RDX: 0000000000000000 RSI: ffffffff84c656a8 RDI: ffffffff8411afe0
RBP: ffff8801ce0b79f0 R08: ffff8801cee0b960 R09: 0000000000000001
R10: 0000000000000000 R11: 1ffff10039dc1727 R12: ffffffff8411afe0
R13: ffffffff846c9620 R14: ffff8801ce0b7ae0 R15: ffffffff84c656a8
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c428f47000 CR3: 00000001c438c000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Stack:
 ffffffff846def20
c ffffffff84c656a8
c 1ffff10039c16f48
c ffff8801ce0b7b08
c
 ffffffff8122e89d
c 00000000000020da
c ffff8801cee0b958
c ffff8801cee0b8b8
c
 ffff8801cee0b960
c ffff8801cee0b8c0
c ffffffff84c656c0
c 1ffff10039c16f48
c
Call Trace:
 [<ffffffff8122e89d>] trace_event_get_offsets_lock include/trace/events/lock.h:38 [inline]
 [<ffffffff8122e89d>] perf_trace_lock+0xdd/0x520 include/trace/events/lock.h:38
 [<ffffffff8123bcef>] trace_lock_release include/trace/events/lock.h:57 [inline]
 [<ffffffff8123bcef>] lock_release+0x8bf/0xb80 kernel/locking/lockdep.c:3774
 [<ffffffff831f2ff0>] seqcount_lockdep_reader_access include/linux/seqlock.h:81 [inline]
 [<ffffffff831f2ff0>] read_seqcount_begin include/linux/seqlock.h:163 [inline]
 [<ffffffff831f2ff0>] nf_conntrack_get_ht include/net/netfilter/nf_conntrack.h:325 [inline]
 [<ffffffff831f2ff0>] gc_worker+0x180/0x620 net/netfilter/nf_conntrack_core.c:968
 [<ffffffff8118d121>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118df16>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119d04d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f9cdc>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Code: 
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c