INFO: task syz-executor7:3872 blocked for more than 140 seconds.
      Not tainted 4.9.119-g9dc978d #23
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor7   D28096  3872      1 0x00000004
 ffff8801d9aee000 0000000000000000 ffff8801bcabca80 ffffffff84629800
 ffff8801db221c18 ffff8801a20174c8 ffffffff839ebdcd ffff8801d9aee8c8
 ffffed003b35dd18 ffff8801d9aee000 00fffc0000000000 ffff8801db2224e8
Call Trace:
 [<ffffffff839ed3cf>] schedule+0x7f/0x1b0 kernel/sched/core.c:3553
 [<ffffffff839edd53>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3586
 [<ffffffff839f21d6>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839f21d6>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff818da421>] vfat_lookup+0xd1/0x530 fs/fat/namei_vfat.c:729
 [<ffffffff8159515e>] lookup_slow+0x23e/0x470 fs/namei.c:1668
 [<ffffffff815a16e6>] walk_component+0x716/0x1bb0 fs/namei.c:1784
 [<ffffffff815a3409>] link_path_walk+0x889/0x1200 fs/namei.c:2120
 [<ffffffff815a447d>] path_openat+0x1ad/0x3590 fs/namei.c:3533
 [<ffffffff815abb27>] do_filp_open+0x197/0x270 fs/namei.c:3568
 [<ffffffff8156e2fd>] do_sys_open+0x30d/0x5c0 fs/open.c:1072
 [<ffffffff8156e5dd>] SYSC_open fs/open.c:1090 [inline]
 [<ffffffff8156e5dd>] SyS_open+0x2d/0x40 fs/open.c:1085
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839fccd3>] 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: [<ffffffff813667bc>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff813667bc>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81426027>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3773:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839fae72>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff821208d2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2142
2 locks held by syz-executor7/3872:
 #0:  (&sb->s_type->i_mutex_key#17){++++++}, at: [<ffffffff81595061>] inode_lock_shared include/linux/fs.h:776 [inline]
 #0:  (&sb->s_type->i_mutex_key#17){++++++}, at: [<ffffffff81595061>] lookup_slow+0x141/0x470 fs/namei.c:1645
 #1:  (&sbi->s_lock){+.+.+.}, at: [<ffffffff818da421>] vfat_lookup+0xd1/0x530 fs/fat/namei_vfat.c:729
1 lock held by syz-executor7/10801:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815d859c>] __fdget_pos+0xac/0xd0 fs/file.c:781

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

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.119-g9dc978d #23
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d857fd08 ffffffff81eb4be9 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b9bd0 ffff8801d857fd40
 ffffffff81ebfee7 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb4be9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb4be9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebfee7>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebfe7a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b9cd4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81366d54>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81366d54>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81366d54>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81366d54>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119d0ed>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839fce9c>] 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: 10754 Comm: syz-executor7 Not tainted 4.9.119-g9dc978d #23
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff880199b88000 task.stack: ffff8801a6250000
RIP: 0010:[<ffffffff81235754>] 
c [<ffffffff81235754>] trace_hardirqs_on_caller+0xc4/0x590 kernel/locking/lockdep.c:2704
RSP: 0018:ffff8801a6257820  EFLAGS: 00000046
RAX: 0000000000000000 RBX: ffff880199b88000 RCX: ffffc900030e9000
RDX: 1ffff10033371112 RSI: ffffffff8162487e RDI: ffff880199b88890
RBP: ffff8801a6257830 R08: ffff880199b88960 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff81624883
R13: dffffc0000000000 R14: ffff8801b67ef888 R15: 000000000000000f
FS:  00007f1dabb30700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f34a8545000 CR3: 00000001c8db2000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 0000000000000010
c 0000000000000000
c ffff8801a6257840
c ffffffff81235c2d
c
 ffff8801a6257890
c ffffffff81624883
c 0000020006ec1a00
c 0000000000000041
c
 ffff8801cbf70000
c 0000000000000001
c ffffea0006ec1a1c
c ffffea0006ec1a00
c
Call Trace:
 [<ffffffff81235c2d>] trace_hardirqs_on+0xd/0x10 kernel/locking/lockdep.c:2743
 [<ffffffff81624883>] lookup_bh_lru fs/buffer.c:1344 [inline]
 [<ffffffff81624883>] __find_get_block+0x183/0x4c0 fs/buffer.c:1356
 [<ffffffff81625749>] __getblk_slow fs/buffer.c:1101 [inline]
 [<ffffffff81625749>] __getblk_gfp+0x189/0x710 fs/buffer.c:1386
 [<ffffffff816290ed>] __bread_gfp+0x2d/0x270 fs/buffer.c:1420
 [<ffffffff818b78e8>] sb_bread include/linux/buffer_head.h:300 [inline]
 [<ffffffff818b78e8>] fat__get_entry+0x4c8/0x8f0 fs/fat/dir.c:100
 [<ffffffff818c095c>] fat_get_entry fs/fat/dir.c:128 [inline]
 [<ffffffff818c095c>] __fat_readdir+0x36c/0x1840 fs/fat/dir.c:589
 [<ffffffff818c1e71>] fat_readdir+0x41/0x50 fs/fat/dir.c:703
 [<ffffffff815b42fc>] iterate_dir+0x1ac/0x600 fs/readdir.c:50
 [<ffffffff815b533c>] SYSC_getdents fs/readdir.c:230 [inline]
 [<ffffffff815b533c>] SyS_getdents+0x13c/0x2a0 fs/readdir.c:211
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839fccd3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
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c