BTRFS error (device loop3): superblock checksum mismatch
BTRFS error (device loop3): open_ctree failed
INFO: task syz-executor7:11066 blocked for more than 120 seconds.
      Not tainted 4.9.107-gdb2c520 #46
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor7   D26952 11066   8099 0x00000004
 ffff8801c2cb0000 0000000000000000 ffff8801da0e2f40 ffff8801812cb000
 ffff8801db221c18 ffff8801d8d47b58 ffffffff839e8c1d 0000000000000002
 0000000041b58ab3 ffffffff843b9ea3 00ffffff81221500 ffff8801db2224e8
Call Trace:
 [<ffffffff839ea21f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff81602a49>] wb_wait_for_completion+0x149/0x1b0 fs/fs-writeback.c:221
 [<ffffffff816081d9>] sync_inodes_sb+0x1a9/0x8d0 fs/fs-writeback.c:2412
 [<ffffffff8161a303>] sync_inodes_one_sb+0x43/0x60 fs/sync.c:73
 [<ffffffff8157cc20>] iterate_supers+0x130/0x260 fs/super.c:593
 [<ffffffff8161ac12>] sys_sync+0xa2/0x170 fs/sync.c:112
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f9b13>] 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: [<ffffffff8136662c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136662c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81425cb7>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3772:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f7cc2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8211fc62>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor7/11066:
 #0:  (&type->s_umount_key#38){++++..}, at: [<ffffffff8157cbd1>] iterate_supers+0xe1/0x260 fs/super.c:591

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

NMI backtrace for cpu 1
CPU: 1 PID: 519 Comm: khungtaskd Not tainted 4.9.107-gdb2c520 #46
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d854fd08 ffffffff81eb3da9 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b96a0 ffff8801d854fd40
 ffffffff81ebf0a7 0000000000000001 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb3da9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb3da9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebf0a7>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebf03a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b97a4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81366bc4>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81366bc4>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81366bc4>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81366bc4>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119d04d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f9cdc>] 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: 4783 Comm: kworker/u4:5 Not tainted 4.9.107-gdb2c520 #46
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn
c (flush-7:0)
c
task: ffff8801812cb000 task.stack: ffff880181300000
RIP: 0010:[<ffffffff81621746>] 
c [<ffffffff81621746>] init_page_buffers+0x266/0x350 fs/buffer.c:970
RSP: 0018:ffff880181307650  EFLAGS: 00000246
RAX: ffff8801812cb000 RBX: dffffc0000000000 RCX: 1ffff1003ac335c1
RDX: 1ffff100380f93e4 RSI: ffffffff81621731 RDI: ffff8801c07c9f20
RBP: ffff880181307690 R08: ffff8801812cb988 R09: 0000000000000001
R10: 0000000000000000 R11: 1ffff1003025972c R12: 0000000000000001
R13: ffff8801c07c9f18 R14: ffff8801d619ae00 R15: ffff8801c07c9f18
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffca39754e0 CR3: 00000001cda7b000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 0000000000000000
c 0000000000000001
c ffffffffffffffff
c 0000000000000003
c
 0000000000000200
c ffffea0006f0ef80
c 0000000000000200
c dffffc0000000000
c
 ffff880181307730
c ffffffff81625549
c ffff880180ef2248
c ffff8801d619ae08
c
Call Trace:
 [<ffffffff81625549>] grow_dev_page fs/buffer.c:1014 [inline]
 [<ffffffff81625549>] grow_buffers fs/buffer.c:1078 [inline]
 [<ffffffff81625549>] __getblk_slow fs/buffer.c:1105 [inline]
 [<ffffffff81625549>] __getblk_gfp+0x579/0x710 fs/buffer.c:1386
 [<ffffffff81628afd>] __bread_gfp+0x2d/0x270 fs/buffer.c:1420
 [<ffffffff818d5d41>] sb_bread include/linux/buffer_head.h:300 [inline]
 [<ffffffff818d5d41>] fat_clusters_flush+0x111/0x380 fs/fat/misc.c:69
 [<ffffffff818cfcd2>] fat_write_inode+0xf2/0x170 fs/fat/inode.c:890
 [<ffffffff8160214d>] write_inode fs/fs-writeback.c:1180 [inline]
 [<ffffffff8160214d>] __writeback_single_inode+0x86d/0x1020 fs/fs-writeback.c:1379
 [<ffffffff8160344c>] writeback_sb_inodes+0x4ac/0xe70 fs/fs-writeback.c:1584
 [<ffffffff81603f0b>] __writeback_inodes_wb+0xfb/0x1e0 fs/fs-writeback.c:1653
 [<ffffffff81604692>] wb_writeback+0x512/0xbd0 fs/fs-writeback.c:1762
 [<ffffffff8160d97e>] wb_do_writeback fs/fs-writeback.c:1894 [inline]
 [<ffffffff8160d97e>] wb_workfn+0x20e/0xdb0 fs/fs-writeback.c:1930
 [<ffffffff8118d121>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118df16>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119d04d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f9cdc>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Code: 
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c