INFO: task syz-executor0:19367 blocked for more than 120 seconds.
      Not tainted 4.9.99-gc2f9bce #22
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D28976 19367  25402 0x00000004
 ffff8801cfcd6000 0000000000000000 ffff8801d4f0aa00 ffffffff84629800
 ffff8801db221b98 ffff8801b1f57cc8 ffffffff839e377d ffff8801cfcd68c8
 ffffed0039f9ad18 ffff8801cfcd6000 00fffc0000000000 ffff8801db222468
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
 [<ffffffff815d567c>] __fdget_pos+0xac/0xd0 fs/file.c:781
 [<ffffffff815b2915>] fdget_pos include/linux/file.h:66 [inline]
 [<ffffffff815b2915>] SYSC_getdents64 fs/readdir.c:309 [inline]
 [<ffffffff815b2915>] SyS_getdents64+0x115/0x280 fs/readdir.c:294
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<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/3658:
 #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-executor0/19367:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815d567c>] __fdget_pos+0xac/0xd0 fs/file.c:781

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

NMI backtrace for cpu 1
CPU: 1 PID: 519 Comm: khungtaskd Not tainted 4.9.99-gc2f9bce #22
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d883fd08 ffffffff81eb0f09 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b7da0 ffff8801d883fd40
 ffffffff81ebc207 0000000000000001 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 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 19358 Comm: syz-executor0 Not tainted 4.9.99-gc2f9bce #22
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801cd358000 task.stack: ffff8801cd720000
RIP: 0010:[<ffffffff8135ca01>] 
c [<ffffffff8135ca01>] __sanitizer_cov_trace_pc+0x1/0x50 kernel/kcov.c:93
RSP: 0018:ffff8801cd727828  EFLAGS: 00000246
RAX: dffffc0000000000 RBX: ffff8801cbf1e910 RCX: ffffc900040f1000
RDX: 1ffff100397e3cf1 RSI: ffffffff8161ecc4 RDI: ffff8801cbf1e910
RBP: ffff8801cd727840 R08: ffff8801cd358960 R09: 0000000000000001
R10: 0000000000000000 R11: 1ffff10039a6b127 R12: 0000000000000000
R13: ffff8801a8c71540 R14: ffff8801cbf1e780 R15: ffffea0006e13680
FS:  00007fcdb74cb700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f203cfffa70 CR3: 00000001b9f6e000 CR4: 00000000001606f0
DR0: 0000000020000000 DR1: 0000000020000000 DR2: 0000000020000000
DR3: 0000000020000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Stack:
 ffff8801cd727840
c ffffffff8162b8cd
c 0000000000000200
c ffff8801cd727890
c
 ffffffff8161ecec
c ffffea0006e13680
c 0000000000000001
c 0000000000000000
c
 0000000000000003
c 0000000000000200
c ffffea0006e13680
c 0000000000000200
c
Call Trace:
 [<ffffffff8161ecec>] init_page_buffers+0xfc/0x350 fs/buffer.c:957
 [<ffffffff81622c59>] grow_dev_page fs/buffer.c:1014 [inline]
 [<ffffffff81622c59>] grow_buffers fs/buffer.c:1078 [inline]
 [<ffffffff81622c59>] __getblk_slow fs/buffer.c:1105 [inline]
 [<ffffffff81622c59>] __getblk_gfp+0x579/0x710 fs/buffer.c:1386
 [<ffffffff8162620d>] __bread_gfp+0x2d/0x270 fs/buffer.c:1420
 [<ffffffff818b3f88>] sb_bread include/linux/buffer_head.h:300 [inline]
 [<ffffffff818b3f88>] fat__get_entry+0x4c8/0x8f0 fs/fat/dir.c:100
 [<ffffffff818bcffc>] fat_get_entry fs/fat/dir.c:128 [inline]
 [<ffffffff818bcffc>] __fat_readdir+0x36c/0x1840 fs/fat/dir.c:589
 [<ffffffff818be511>] fat_readdir+0x41/0x50 fs/fat/dir.c:703
 [<ffffffff815b165c>] iterate_dir+0x1ac/0x600 fs/readdir.c:50
 [<ffffffff815b2937>] SYSC_getdents64 fs/readdir.c:313 [inline]
 [<ffffffff815b2937>] SyS_getdents64+0x137/0x280 fs/readdir.c:294
 [<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