loop0: rw=0, want=18442984958116442982, limit=264192
attempt to access beyond end of device
loop0: rw=0, want=18442984958116442984, limit=264192
attempt to access beyond end of device
loop0: rw=0, want=18442984958116442986, limit=264192
INFO: task syz-executor4:20490 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-executor4   D29560 20490  17202 0x00000004
 ffff8801b849e000 0000000000000000 ffff8801d467ea00 ffff8801d41e1800
 ffff8801db321c18 ffff8801985a7b58 ffffffff839ebdcd 0000000000000002
 0000000041b58ab3 ffffffff843bc37b 00ffffff81221590 ffff8801db3224e8
Call Trace:
 [<ffffffff839ed3cf>] schedule+0x7f/0x1b0 kernel/sched/core.c:3553
 [<ffffffff81603039>] wb_wait_for_completion+0x149/0x1b0 fs/fs-writeback.c:221
 [<ffffffff816087c9>] sync_inodes_sb+0x1a9/0x8d0 fs/fs-writeback.c:2412
 [<ffffffff8161a8f3>] sync_inodes_one_sb+0x43/0x60 fs/sync.c:73
 [<ffffffff8157d1b0>] iterate_supers+0x130/0x260 fs/super.c:593
 [<ffffffff8161b202>] sys_sync+0xa2/0x170 fs/sync.c:112
 [<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 rs:main Q:Reg/3670:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815d859c>] __fdget_pos+0xac/0xd0 fs/file.c:781
 #1:  (sb_writers#3){.+.+.+}, at: [<ffffffff8157307e>] file_start_write include/linux/fs.h:2640 [inline]
 #1:  (sb_writers#3){.+.+.+}, at: [<ffffffff8157307e>] vfs_write+0x3ae/0x530 fs/read_write.c:556
2 locks held by getty/3768:
 #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
1 lock held by syz-executor4/20490:
 #0:  (&type->s_umount_key#44){++++..}, at: [<ffffffff8157d161>] iterate_supers+0xe1/0x260 fs/super.c:591
1 lock held by syz-executor4/20498:
 #0:  (&type->s_umount_key#44){++++..}, at: [<ffffffff8157d161>] iterate_supers+0xe1/0x260 fs/super.c:591

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

NMI backtrace for cpu 1
CPU: 1 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
 ffff8801d865fd08 ffffffff81eb4be9 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b9bd0 ffff8801d865fd40
 ffffffff81ebfee7 0000000000000001 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 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 215 Comm: kworker/u4:2 Not tainted 4.9.119-g9dc978d #23
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn
c (flush-7:0)
c
task: ffff8801d8c30000 task.stack: ffff8801d8c38000
RIP: 0010:[<ffffffff8127f68a>] 
c [<ffffffff8127f68a>] __read_once_size include/linux/compiler.h:243 [inline]
RIP: 0010:[<ffffffff8127f68a>] 
c [<ffffffff8127f68a>] atomic_read arch/x86/include/asm/atomic.h:26 [inline]
RIP: 0010:[<ffffffff8127f68a>] 
c [<ffffffff8127f68a>] __rcu_is_watching kernel/rcu/tree.c:1053 [inline]
RIP: 0010:[<ffffffff8127f68a>] 
c [<ffffffff8127f68a>] rcu_is_watching+0x5a/0xa0 kernel/rcu/tree.c:1067
RSP: 0018:ffff8801d8c3f5b0  EFLAGS: 00000a03
RAX: dffffc0000000000 RBX: ffff8801db21a71c RCX: 1ffffffff0886880
RDX: 0000000000000000 RSI: ffffffff81f1c62b RDI: ffffffff84434400
RBP: ffff8801d8c3f5c0 R08: ffff8801d8c30988 R09: 0000000000000001
R10: ffff8801d8c30000 R11: 1ffff1003b18612c R12: ffff8801962ab1a8
R13: dffffc0000000000 R14: 0000000002420848 R15: ffff8801d5d98f08
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f09de692000 CR3: 00000001b76d6000 CR4: 00000000001606f0
DR0: 0000000020000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Stack:
 5355abbd3fbc68ea
c ffffea0006502700
c ffff8801d8c3f5d0
c ffffffff8127c227
c
 ffff8801d8c3f638
c ffffffff814391bb
c ffffffff81438e70
c ffffffff81624533
c
 ffff8801d5d98dd4
c 0000000000000000
c ffff8801d5d98f10
c ffffea0006502700
c
Call Trace:
 [<ffffffff8127c227>] rcu_read_lock_held+0x87/0xc0 kernel/rcu/update.c:293
 [<ffffffff814391bb>] radix_tree_deref_slot include/linux/radix-tree.h:199 [inline]
 [<ffffffff814391bb>] find_get_entry+0x34b/0x540 mm/filemap.c:1095
 [<ffffffff8143a2eb>] pagecache_get_page+0x4b/0x720 mm/filemap.c:1201
 [<ffffffff81625809>] find_or_create_page include/linux/pagemap.h:309 [inline]
 [<ffffffff81625809>] grow_dev_page fs/buffer.c:1005 [inline]
 [<ffffffff81625809>] grow_buffers fs/buffer.c:1078 [inline]
 [<ffffffff81625809>] __getblk_slow fs/buffer.c:1105 [inline]
 [<ffffffff81625809>] __getblk_gfp+0x249/0x710 fs/buffer.c:1386
 [<ffffffff816290ed>] __bread_gfp+0x2d/0x270 fs/buffer.c:1420
 [<ffffffff818d69e1>] sb_bread include/linux/buffer_head.h:300 [inline]
 [<ffffffff818d69e1>] fat_clusters_flush+0x111/0x380 fs/fat/misc.c:69
 [<ffffffff818d0942>] fat_write_inode+0xf2/0x170 fs/fat/inode.c:898
 [<ffffffff8160273d>] write_inode fs/fs-writeback.c:1180 [inline]
 [<ffffffff8160273d>] __writeback_single_inode+0x86d/0x1020 fs/fs-writeback.c:1379
 [<ffffffff81603a3c>] writeback_sb_inodes+0x4ac/0xe70 fs/fs-writeback.c:1584
 [<ffffffff816044fb>] __writeback_inodes_wb+0xfb/0x1e0 fs/fs-writeback.c:1653
 [<ffffffff81604c82>] wb_writeback+0x512/0xbd0 fs/fs-writeback.c:1762
 [<ffffffff8160df6e>] wb_do_writeback fs/fs-writeback.c:1894 [inline]
 [<ffffffff8160df6e>] wb_workfn+0x20e/0xdb0 fs/fs-writeback.c:1930
 [<ffffffff8118d181>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff8118df76>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119d0ed>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839fce9c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Code: 
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c<48> 
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c