BUG: workqueue lockup - pool[  429.311924] INFO: task syz-executor3:2116 blocked for more than 140 seconds.
      Not tainted 4.9.129+ #43
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor3   D
27672  2116      1 0x00000004
 ffff8801a441e880 ffff8801c8468000 ffff8801ca8c97c0 ffff8801db721018
 ffff8801a8637658 ffffffff827e7d32 0000000000000001 ffff8801d0963830
 ffffed003a12c705 00ff8801d0962f80 ffff8801db7218f0Call Trace:
 [<ffffffff827e925f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3553
 [<ffffffff827e9be3>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3586
 [<ffffffff827ebc5d>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff827ebc5d>] mutex_lock_nested+0x38d/0x900 kernel/locking/mutex.c:621
 [<ffffffff81dc9edb>] lo_open+0x1b/0xa0 drivers/block/loop.c:1564
 [<ffffffff815c87c3>] __blkdev_get+0x263/0xd60 fs/block_dev.c:1282
 [<ffffffff815cb49a>] blkdev_get+0x2da/0x920 fs/block_dev.c:1416
 [<ffffffff815cbcf5>] blkdev_open+0x1a5/0x250 fs/block_dev.c:1571
 [<ffffffff81501baf>] do_dentry_open+0x3ef/0xc90 fs/open.c:766
 [<ffffffff815054dc>] vfs_open+0x11c/0x210 fs/open.c:879
 [<ffffffff8153c2b2>] do_last fs/namei.c:3410 [inline]
 [<ffffffff8153c2b2>] path_openat+0x542/0x2790 fs/namei.c:3534
 [<ffffffff81541387>] do_filp_open+0x197/0x270 fs/namei.c:3568
 [<ffffffff81505eed>] do_sys_open+0x30d/0x5c0 fs/open.c:1072
 [<ffffffff815061cd>] SYSC_open fs/open.c:1090 [inline]
 [<ffffffff815061cd>] SyS_open+0x2d/0x40 fs/open.c:1085
 [<ffffffff810056ef>] do_syscall_64+0x19f/0x550 arch/x86/entry/common.c:285
 [<ffffffff827f7f93>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Showing all locks held in the system:
2 locks held by khungtaskd/24:
 #0: 
 (rcu_read_lock){......}, at: [<ffffffff8131b83c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 (rcu_read_lock){......}, at: [<ffffffff8131b83c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 (tasklist_lock){.+.+..}, at: [<ffffffff813fdfe4>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
 #0: 
 (&f->f_pos_lock){+.+.+.}, at: [<ffffffff8156c9ec>] __fdget_pos+0xac/0xd0 fs/file.c:781
 #0: 
 (&tty->ldisc_sem){++++++}, at: [<ffffffff827f6082>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff81d1fe52>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2142
 #0: 
 (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff815c866c>] __blkdev_get+0x10c/0xd60 fs/block_dev.c:1268
 (loop_index_mutex){+.+.+.}, at: [<ffffffff81dc9edb>] lo_open+0x1b/0xa0 drivers/block/loop.c:1564
 #0: 
 (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff815c866c>] __blkdev_get+0x10c/0xd60 fs/block_dev.c:1268
 (loop_index_mutex){+.+.+.}, at: [<ffffffff81dc9edb>] lo_open+0x1b/0xa0 drivers/block/loop.c:1564
 #0: 
 (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff815c866c>] __blkdev_get+0x10c/0xd60 fs/block_dev.c:1268
 (loop_index_mutex){+.+.+.}, at: [<ffffffff81dc9edb>] lo_open+0x1b/0xa0 drivers/block/loop.c:1564
 #0: 
 (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff815c866c>] __blkdev_get+0x10c/0xd60 fs/block_dev.c:1268
 (loop_index_mutex){+.+.+.}, at: [<ffffffff81dc9edb>] lo_open+0x1b/0xa0 drivers/block/loop.c:1564
 #0: 
 (loop_index_mutex){+.+.+.}, at: [<ffffffff81dd1b0a>] loop_control_ioctl+0x7a/0x300 drivers/block/loop.c:1915
 (rcu_preempt_state.exp_mutex){+.+...}, at: [<ffffffff81249ee9>] exp_funnel_lock kernel/rcu/tree_exp.h:256 [inline]
 (rcu_preempt_state.exp_mutex){+.+...}, at: [<ffffffff81249ee9>] _synchronize_rcu_expedited+0x339/0x840 kernel/rcu/tree_exp.h:569
 #0: 
 (loop_index_mutex){+.+.+.}, at: [<ffffffff81dd1b0a>] loop_control_ioctl+0x7a/0x300 drivers/block/loop.c:1915
 #0: 
 (loop_index_mutex){+.+.+.}, at: [<ffffffff81dd1b0a>] loop_control_ioctl+0x7a/0x300 drivers/block/loop.c:1915
 #0: 
 (loop_index_mutex){+.+.+.}, at: [<ffffffff81dd1b0a>] loop_control_ioctl+0x7a/0x300 drivers/block/loop.c:1915
=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 24 Comm: khungtaskd Not tainted 4.9.129+ #43
 ffff8801d9907d08
 ffffffff81b2bbb9 0000000000000000 0000000000000001 0000000000000001
 0000000000000001 ffffffff81098180 ffff8801d9907d40 ffffffff81b36cc9
 0000000000000001 0000000000000000 0000000000000003Call Trace:
 [<ffffffff81b2bbb9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81b2bbb9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81b36cc9>] nmi_cpu_backtrace.cold.0+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81b36c5c>] nmi_trigger_cpumask_backtrace+0x12c/0x151 lib/nmi_backtrace.c:60
 [<ffffffff81098284>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff8131bdcd>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff8131bdcd>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff8131bdcd>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff8131bdcd>] watchdog+0x6ad/0xa20 kernel/hung_task.c:239
 [<ffffffff8114272d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff827f815c>] 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: 351 Comm: kworker/0:2 Not tainted 4.9.129+ #43
Workqueue: events rtc_timer_do_work
c
task: ffff8801d6545f00 task.stack: ffff8801d51a8000
RIP: 0010:[<ffffffff81d4b20b>] 
c [<ffffffff81d4b20b>] inb arch/x86/include/asm/io.h:316 [inline]
RIP: 0010:[<ffffffff81d4b20b>] 
c [<ffffffff81d4b20b>] io_serial_in+0x6b/0x90 drivers/tty/serial/8250/8250_port.c:413
RSP: 0000:ffff8801db607790  EFLAGS: 00000002
RAX: dffffc0000000020 RBX: 00000000000003fd RCX: 0000000000000000
RDX: 00000000000003fd RSI: ffffffff81d4b1b1 RDI: ffffffff84b5ba18
RBP: ffff8801db6077a0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff84b5b9e0
R13: 0000000000000020 R14: fffffbfff096b783 R15: fffffbfff096b745
FS:  0000000000000000(0000) GS:ffff8801db600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000001f5f308 CR3: 000000000301e000 CR4: 00000000001606b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff84b5b9e0
c 0000000000002707
c ffff8801db6077f0
c ffffffff81d4d424
c
 1ffff1003b6c0ef9
c ffffffff84b5ba28
c ffffffff84b5bc1a
c ffffffff84b5b9e0
c
 0000000000000038
c ffffffff81d4d570
c dffffc0000000000
c 0000000000000038
c
Call Trace:
 <IRQ> 
d [<ffffffff81d4d424>] serial_in drivers/tty/serial/8250/8250.h:111 [inline]
 <IRQ> 
d [<ffffffff81d4d424>] wait_for_xmitr+0x94/0x1e0 drivers/tty/serial/8250/8250_port.c:1997
 [<ffffffff81d4d58f>] serial8250_console_putchar+0x1f/0x60 drivers/tty/serial/8250/8250_port.c:3103
 [<ffffffff81d359a9>] uart_console_write+0x59/0xf0 drivers/tty/serial/serial_core.c:1866
 [<ffffffff81d587a8>] serial8250_console_write+0x528/0x820 drivers/tty/serial/8250/8250_port.c:3169
 [<ffffffff81d461bf>] univ8250_console_write+0x5f/0x70 drivers/tty/serial/8250/8250_core.c:594
 [<ffffffff812230cd>] call_console_drivers.isra.0.constprop.15+0x1ad/0x360 kernel/printk/printk.c:1589
 [<ffffffff81225afe>] console_cont_flush kernel/printk/printk.c:2316 [inline]
 [<ffffffff81225afe>] console_unlock+0x17e/0xb50 kernel/printk/printk.c:2382
 [<ffffffff81226918>] vprintk_emit+0x448/0x790 kernel/printk/printk.c:1903
 [<ffffffff81226c88>] vprintk+0x28/0x30 kernel/printk/printk.c:1913
 [<ffffffff81226cad>] vprintk_default+0x1d/0x30 kernel/printk/printk.c:1914
 [<ffffffff81402b72>] vprintk_func kernel/printk/internal.h:36 [inline]
 [<ffffffff81402b72>] printk+0xaf/0xd7 kernel/printk/printk.c:1975
 [<ffffffff813f921f>] wq_watchdog_timer_fn.cold.24+0x11/0x65 kernel/workqueue.c:5393
 [<ffffffff812621c3>] call_timer_fn+0x163/0x6e0 kernel/time/timer.c:1319
 [<ffffffff81262974>] expire_timers+0x234/0x580 kernel/time/timer.c:1359
 [<ffffffff812630c5>] __run_timers kernel/time/timer.c:1674 [inline]
 [<ffffffff812630c5>] run_timer_softirq+0x405/0x5e0 kernel/time/timer.c:1689
 [<ffffffff827fd280>] __do_softirq+0x210/0x940 kernel/softirq.c:288
 [<ffffffff810ef974>] invoke_softirq kernel/softirq.c:368 [inline]
 [<ffffffff810ef974>] irq_exit+0x114/0x150 kernel/softirq.c:409
 [<ffffffff827fbe61>] exiting_irq arch/x86/include/asm/apic.h:669 [inline]
 [<ffffffff827fbe61>] smp_apic_timer_interrupt+0x81/0xa0 arch/x86/kernel/apic/apic.c:962
 [<ffffffff827f972d>] apic_timer_interrupt+0x9d/0xb0 arch/x86/entry/entry_64.S:648
 <EOI> 
d [<ffffffff827f76ef>] ? arch_local_irq_restore arch/x86/include/asm/paravirt.h:768 [inline]
 <EOI> 
d [<ffffffff827f76ef>] ? __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:162 [inline]
 <EOI> 
d [<ffffffff827f76ef>] ? _raw_spin_unlock_irqrestore+0x5f/0x70 kernel/locking/spinlock.c:191
 [<ffffffff82071591>] spin_unlock_irqrestore include/linux/spinlock.h:362 [inline]
 [<ffffffff82071591>] rtc_handle_legacy_irq+0x81/0x190 drivers/rtc/interface.c:515
 [<ffffffff820716ef>] rtc_uie_update_irq+0x1f/0x30 drivers/rtc/interface.c:550
 [<ffffffff820719df>] rtc_timer_do_work+0x1ff/0x5e0 drivers/rtc/interface.c:881
 [<ffffffff81130bb1>] process_one_work+0x831/0x1530 kernel/workqueue.c:2092
 [<ffffffff81131986>] worker_thread+0xd6/0x1140 kernel/workqueue.c:2226
 [<ffffffff8114272d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff827f815c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Code: 
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