FAT-fs (loop4): bogus number of reserved sectors
FAT-fs (loop4): Can't find a valid FAT filesystem
INFO: task syz-executor5:17096 blocked for more than 140 seconds.
      Not tainted 4.9.112-gf540ce0 #8
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor5   D29480 17096   7714 0x00000004
 ffff88019c65e000 ffff8801c07ff9c0 ffff8801ccaa9f80 ffff88019b9c0000
 ffff8801db321c18 ffff8801bbe07b58 ffffffff839e907d 0000000000000002
 0000000041b58ab3 ffffffff843bb23b 00ffffff81221570 ffff8801db3224e8
Call Trace:
 [<ffffffff839ea67f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff81602c29>] wb_wait_for_completion+0x149/0x1b0 fs/fs-writeback.c:221
 [<ffffffff816083b9>] sync_inodes_sb+0x1a9/0x8d0 fs/fs-writeback.c:2412
 [<ffffffff8161a4e3>] sync_inodes_one_sb+0x43/0x60 fs/sync.c:73
 [<ffffffff8157ce00>] iterate_supers+0x130/0x260 fs/super.c:593
 [<ffffffff8161adf2>] sys_sync+0xa2/0x170 fs/sync.c:112
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f9f53>] 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: [<ffffffff8136675c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136675c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81425de7>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3783:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f8122>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211edc2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2142
1 lock held by syz-executor5/17096:
 #0:  (&type->s_umount_key#38){++++..}, at: [<ffffffff8157cdb1>] iterate_supers+0xe1/0x260 fs/super.c:591

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

NMI backtrace for cpu 1
CPU: 1 PID: 519 Comm: khungtaskd Not tainted 4.9.112-gf540ce0 #8
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8647d08 ffffffff81eb3249 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b9bd0 ffff8801d8647d40
 ffffffff81ebe547 0000000000000001 0000000000000000 0000000000000002
Call Trace:
 [<ffffffff81eb3249>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb3249>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebe547>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebe4da>] 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
 [<ffffffff81366cf4>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81366cf4>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81366cf4>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81366cf4>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119d0bd>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839fa11c>] 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: 5340 Comm: kworker/u4:7 Not tainted 4.9.112-gf540ce0 #8
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn
c (flush-7:0)
c
task: ffff8801bbc6c800 task.stack: ffff880199690000
RIP: 0010:[<ffffffff8123566b>] 
c [<ffffffff8123566b>] mark_held_locks+0xcb/0x130 kernel/locking/lockdep.c:2660
RSP: 0018:ffff8801996975d0  EFLAGS: 00000002
RAX: 0000000000000001 RBX: 0000000000000003 RCX: 1ffff1003778da2c
RDX: 1ffffffff0ac1802 RSI: ffff8801bbc6d140 RDI: ffffffff8560c010
RBP: ffff880199697610 R08: ffff8801bbc6d160 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801bbc6d0c8
R13: ffffed003778da18 R14: ffff8801bbc6c800 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fecf37eb000 CR3: 00000001cb640000 CR4: 00000000001606f0
DR0: 0000000020000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Stack:
 ffff8801bbc6c800
c ffff8801bbc6d0c0
c 0000000600000007
c ffff8801bbc6c800
c
 ffffffff81624473
c dffffc0000000000
c ffff8801b63327e0
c 000000000000000f
c
 ffff880199697630
c ffffffff81235a5b
c 0000000000000010
c 0000000000000000
c
Call Trace:
 [<ffffffff81235a5b>] __trace_hardirqs_on_caller kernel/locking/lockdep.c:2689 [inline]
 [<ffffffff81235a5b>] trace_hardirqs_on_caller+0x38b/0x590 kernel/locking/lockdep.c:2736
 [<ffffffff81235c6d>] trace_hardirqs_on+0xd/0x10 kernel/locking/lockdep.c:2743
 [<ffffffff81624473>] lookup_bh_lru fs/buffer.c:1344 [inline]
 [<ffffffff81624473>] __find_get_block+0x183/0x4c0 fs/buffer.c:1356
 [<ffffffff81625339>] __getblk_slow fs/buffer.c:1101 [inline]
 [<ffffffff81625339>] __getblk_gfp+0x189/0x710 fs/buffer.c:1386
 [<ffffffff81628cdd>] __bread_gfp+0x2d/0x270 fs/buffer.c:1420
 [<ffffffff818d68d1>] sb_bread include/linux/buffer_head.h:300 [inline]
 [<ffffffff818d68d1>] fat_clusters_flush+0x111/0x380 fs/fat/misc.c:69
 [<ffffffff818d0862>] fat_write_inode+0xf2/0x170 fs/fat/inode.c:890
 [<ffffffff8160232d>] write_inode fs/fs-writeback.c:1180 [inline]
 [<ffffffff8160232d>] __writeback_single_inode+0x86d/0x1020 fs/fs-writeback.c:1379
 [<ffffffff8160362c>] writeback_sb_inodes+0x4ac/0xe70 fs/fs-writeback.c:1584
 [<ffffffff816040eb>] __writeback_inodes_wb+0xfb/0x1e0 fs/fs-writeback.c:1653
 [<ffffffff81604872>] wb_writeback+0x512/0xbd0 fs/fs-writeback.c:1762
 [<ffffffff8160db5e>] wb_do_writeback fs/fs-writeback.c:1894 [inline]
 [<ffffffff8160db5e>] wb_workfn+0x20e/0xdb0 fs/fs-writeback.c:1930
 [<ffffffff8118d191>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118df86>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119d0bd>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839fa11c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Code: 
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c