INFO: task syz-executor1:10583 blocked for more than 120 seconds.
      Not tainted 4.9.99-gc2f9bce #25
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor1   D28488 10583   3871 0x00000002
 ffff8801d0141800 0000000000000000 ffff8801d9bd9f80 ffff8801d9a6b000
 ffff8801db321b98 ffff8801b8d67838 ffffffff839e377d ffff8801d01420c8
 ffffed003a028418 ffff8801d0141800 00fffc0000000000 ffff8801db322468
Call Trace:
 [<ffffffff839e4d7f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839e5703>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839e9b86>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839e9b86>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff82f496ff>] seq_free_client+0x1f/0xf0 sound/core/seq/seq_clientmgr.c:277
 [<ffffffff82f498c1>] snd_seq_release+0x51/0xe0 sound/core/seq/seq_clientmgr.c:367
 [<ffffffff815759f3>] __fput+0x263/0x700 fs/file_table.c:208
 [<ffffffff81575f15>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8119603c>] task_work_run+0x10c/0x180 kernel/task_work.c:116
 [<ffffffff8113ec91>] exit_task_work include/linux/task_work.h:21 [inline]
 [<ffffffff8113ec91>] do_exit+0x9e1/0x27c0 kernel/exit.c:837
 [<ffffffff81144d91>] do_group_exit+0x111/0x340 kernel/exit.c:941
 [<ffffffff81167b8f>] get_signal+0x4cf/0x1450 kernel/signal.c:2317
 [<ffffffff810524d7>] do_signal+0x87/0x19f0 arch/x86/kernel/signal.c:807
 [<ffffffff81005581>] exit_to_usermode_loop+0xe1/0x120 arch/x86/entry/common.c:157
 [<ffffffff810064d4>] prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline]
 [<ffffffff810064d4>] syscall_return_slowpath arch/x86/entry/common.c:260 [inline]
 [<ffffffff810064d4>] do_syscall_64+0x364/0x490 arch/x86/entry/common.c:287
 [<ffffffff839f4653>] 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: [<ffffffff813646ec>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff813646ec>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81423bc0>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3771:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f2822>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8211cc32>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor1/10583:
 #0:  (register_mutex#3){+.+.+.}, at: [<ffffffff82f496ff>] seq_free_client+0x1f/0xf0 sound/core/seq/seq_clientmgr.c:277
1 lock held by syz-executor6/16226:
 #0:  (register_mutex#3){+.+.+.}, at: [<ffffffff82f4aa25>] snd_seq_open+0x45/0x570 sound/core/seq/seq_clientmgr.c:314

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

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.99-gc2f9bce #25
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d850fd08 ffffffff81eb0f09 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b7da0 ffff8801d850fd40
 ffffffff81ebc207 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb0f09>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb0f09>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebc207>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebc19a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b7ea4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81364c84>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81364c84>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81364c84>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81364c84>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119ad5d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f481c>] 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: 16277 Comm: syz-executor3 Not tainted 4.9.99-gc2f9bce #25
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801a005c800 task.stack: ffff880199530000
RIP: 0010:[<ffffffff811b9082>] 
c [<ffffffff811b9082>] ___might_sleep+0x42/0x260 kernel/sched/core.c:7958
RSP: 0018:ffff880199537ca0  EFLAGS: 00000246
RAX: 0000000000000000 RBX: ffff8801a005c800 RCX: ffffc90001755000
RDX: 0000000000000000 RSI: 00000000000002d7 RDI: 0000000000000246
RBP: ffff880199537cc8 R08: ffffed00332a6fb9 R09: ffffed00332a6fb1
R10: ffffed00332a6fb8 R11: ffff880199537dc7 R12: 0000000000000000
R13: ffffffff83ea5c80 R14: 00000000000002d7 R15: 000000007fffffff
FS:  00007f5d33013700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020e00000 CR3: 00000001b80bc000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801a005c800
c ffffffff83ea5c80
c 00000000000002d7
c 0000000000000000
c
 000000007fffffff
c ffff880199537d08
c ffffffff811b9335
c ffff880199537ce8
c
 0000000000000286
c ffff8801a005c800
c ffffffff83ea5c80
c 00000000000002d7
c
Call Trace:
 [<ffffffff811b9335>] __might_sleep+0x95/0x1a0 kernel/sched/core.c:7949
 [<ffffffff814be35f>] __might_fault+0xaf/0x1d0 mm/memory.c:4011
 [<ffffffff82176ee5>] copy_to_user arch/x86/include/asm/uaccess.h:727 [inline]
 [<ffffffff82176ee5>] extract_crng_user drivers/char/random.c:1014 [inline]
 [<ffffffff82176ee5>] urandom_read+0x1d5/0x580 drivers/char/random.c:1805
 [<ffffffff82177f0d>] SYSC_getrandom drivers/char/random.c:1957 [inline]
 [<ffffffff82177f0d>] SyS_getrandom+0xcd/0x280 drivers/char/random.c:1938
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f4653>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
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c<65> 
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c