INFO: task syz-executor3:3863 blocked for more than 140 seconds.
      Not tainted 4.9.123-g8dd3fc2 #27
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor3   D27672  3863      1 0x00000004
 ffff8801d55b4800 0000000000000000 ffff8801cd0f4fc0 ffffffff84629800
 ffff8801db221c18 ffff8801a0e474c8 ffffffff839f0dbd ffff8801d55b50c8
 ffffed003aab6a18 ffff8801d55b4800 00fffc0000000000 ffff8801db2224e8
Call Trace:
 [<ffffffff839f23bf>] schedule+0x7f/0x1b0 kernel/sched/core.c:3553
 [<ffffffff839f2d43>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3586
 [<ffffffff839f71c6>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839f71c6>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff818df251>] vfat_lookup+0xd1/0x530 fs/fat/namei_vfat.c:729
 [<ffffffff815995de>] lookup_slow+0x23e/0x470 fs/namei.c:1668
 [<ffffffff815a5b66>] walk_component+0x716/0x1bb0 fs/namei.c:1784
 [<ffffffff815a7889>] link_path_walk+0x889/0x1200 fs/namei.c:2120
 [<ffffffff815a88fd>] path_openat+0x1ad/0x3590 fs/namei.c:3533
 [<ffffffff815affa7>] do_filp_open+0x197/0x270 fs/namei.c:3568
 [<ffffffff8157277d>] do_sys_open+0x30d/0x5c0 fs/open.c:1072
 [<ffffffff81572a5d>] SYSC_open fs/open.c:1090 [inline]
 [<ffffffff81572a5d>] SyS_open+0x2d/0x40 fs/open.c:1085
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff83a01c93>] 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: [<ffffffff81368a9c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff81368a9c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.?..}, at: [<ffffffff81428308>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3762:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839ffe62>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff821253c2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2142
2 locks held by syz-executor3/3863:
 #0:  (&sb->s_type->i_mutex_key#17){++++++}, at: [<ffffffff815994e1>] inode_lock_shared include/linux/fs.h:776 [inline]
 #0:  (&sb->s_type->i_mutex_key#17){++++++}, at: [<ffffffff815994e1>] lookup_slow+0x141/0x470 fs/namei.c:1645
 #1:  (&sbi->s_lock){+.+.+.}, at: [<ffffffff818df251>] vfat_lookup+0xd1/0x530 fs/fat/namei_vfat.c:729

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

NMI backtrace for cpu 1
CPU: 1 PID: 519 Comm: khungtaskd Not tainted 4.9.123-g8dd3fc2 #27
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d85cfd08 ffffffff81eb9689 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b9fa0 ffff8801d85cfd40
 ffffffff81ec49c7 0000000000000001 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb9689>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb9689>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ec49c7>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ec495a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810ba0a4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81369034>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81369034>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81369034>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81369034>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119f3cd>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff83a01e5c>] 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: 24990 Comm: syz-executor3 Not tainted 4.9.123-g8dd3fc2 #27
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff88019cf76000 task.stack: ffff8801c3e90000
RIP: 0010:[<ffffffff81360dfb>] 
c [<ffffffff81360dfb>] __write_once_size include/linux/compiler.h:272 [inline]
RIP: 0010:[<ffffffff81360dfb>] 
c [<ffffffff81360dfb>] __sanitizer_cov_trace_pc+0x4b/0x50 kernel/kcov.c:108
RSP: 0018:ffff8801c3e97268  EFLAGS: 00000246
RAX: 0000000000040000 RBX: dffffc0000000000 RCX: ffffc90003ee8000
RDX: 0000000000040000 RSI: ffffffff81626161 RDI: ffff8801b84cd938
RBP: ffff8801c3e97268 R08: ffff88019cf76938 R09: 0000000000000001
R10: 0000000000000000 R11: 1ffff100339eed22 R12: 0000000000000043
R13: ffff8801b84cda80 R14: ffff8801cbf98b80 R15: ffff8801b84cd888
FS:  00007f01d5623700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fbb8e93d140 CR3: 00000001badfb000 CR4: 00000000001606f0
DR0: 0000000020000000 DR1: 0000000020000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Stack:
 ffff8801c3e972b8
c ffffffff81626161
c 0000000008100000
c 0000000000000001
c
 0000000000040800
c 0000000000000003
c 0000000000000200
c ffffea0006eeed40
c
 0000000000000200
c dffffc0000000000
c ffff8801c3e97358
c ffffffff81629f79
c
Call Trace:
 [<ffffffff81626161>] init_page_buffers+0x251/0x350 fs/buffer.c:969
 [<ffffffff81629f79>] grow_dev_page fs/buffer.c:1014 [inline]
 [<ffffffff81629f79>] grow_buffers fs/buffer.c:1078 [inline]
 [<ffffffff81629f79>] __getblk_slow fs/buffer.c:1105 [inline]
 [<ffffffff81629f79>] __getblk_gfp+0x579/0x710 fs/buffer.c:1386
 [<ffffffff8162d52d>] __bread_gfp+0x2d/0x270 fs/buffer.c:1420
 [<ffffffff818bc718>] sb_bread include/linux/buffer_head.h:300 [inline]
 [<ffffffff818bc718>] fat__get_entry+0x4c8/0x8f0 fs/fat/dir.c:100
 [<ffffffff818c4517>] fat_get_entry fs/fat/dir.c:128 [inline]
 [<ffffffff818c4517>] fat_search_long+0x277/0x1180 fs/fat/dir.c:477
 [<ffffffff818dea84>] vfat_find+0x134/0x180 fs/fat/namei_vfat.c:708
 [<ffffffff818df261>] vfat_lookup+0xe1/0x530 fs/fat/namei_vfat.c:731
 [<ffffffff8159f9dd>] lookup_open+0x63d/0x1930 fs/namei.c:3203
 [<ffffffff815a9f53>] do_last fs/namei.c:3315 [inline]
 [<ffffffff815a9f53>] path_openat+0x1803/0x3590 fs/namei.c:3534
 [<ffffffff815affa7>] do_filp_open+0x197/0x270 fs/namei.c:3568
 [<ffffffff8157277d>] do_sys_open+0x30d/0x5c0 fs/open.c:1072
 [<ffffffff81572a5d>] SYSC_open fs/open.c:1090 [inline]
 [<ffffffff81572a5d>] SyS_open+0x2d/0x40 fs/open.c:1085
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff83a01c93>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
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c<5d> 
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c