protocol 8906 is buggy, dev sit0
INFO: task syz-executor2:8592 blocked for more than 120 seconds.
      Not tainted 4.9.101-gaef17a5 #29
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor2   D28456  8592   8176 0x00000004
 ffff880192f8c800 ffff8801bf558a80 ffff8801cc496a00 ffff8801b63fb000
 ffff8801db221b98 ffff880188a67c10 ffffffff839e39bd ffff8801ccad5588
 0000000000000000 0000000000000000 0000000000000000 ffff8801db222468
Call Trace:
 [<ffffffff839e4fbf>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839ef3e4>] rwsem_down_read_failed+0x1e4/0x320 kernel/locking/rwsem-xadd.c:260
 [<ffffffff81ee52b8>] call_rwsem_down_read_failed+0x18/0x30 arch/x86/lib/rwsem.S:94
 [<ffffffff839ee312>] __down_read arch/x86/include/asm/rwsem.h:65 [inline]
 [<ffffffff839ee312>] down_read+0x52/0xb0 kernel/locking/rwsem.c:24
 [<ffffffff8157a5f1>] iterate_supers+0xe1/0x260 fs/super.c:591
 [<ffffffff81618412>] sys_sync+0xa2/0x170 fs/sync.c:112
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f4893>] 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: [<ffffffff8136477c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136477c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81423c90>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3774:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f2a62>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211cd32>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor2/8592:
 #0:  (&type->s_umount_key#44){++++..}, at: [<ffffffff8157a5f1>] iterate_supers+0xe1/0x260 fs/super.c:591
1 lock held by syz-executor2/8618:
 #0:  (&type->s_umount_key#44){++++..}, at: [<ffffffff8157a5f1>] iterate_supers+0xe1/0x260 fs/super.c:591

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

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.101-gaef17a5 #29
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d85ffd08 ffffffff81eb1009 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b7da0 ffff8801d85ffd40
 ffffffff81ebc307 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb1009>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb1009>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebc307>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebc29a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b7ea4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81364d14>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81364d14>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81364d14>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81364d14>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119ad9d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f4a5c>] 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: 8585 Comm: syz-executor0 Not tainted 4.9.101-gaef17a5 #29
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff880192f88000 task.stack: ffff88018b410000
RIP: 0010:[<ffffffff81234552>] 
c [<ffffffff81234552>] atomic_inc arch/x86/include/asm/atomic.h:91 [inline]
RIP: 0010:[<ffffffff81234552>] 
c [<ffffffff81234552>] __lock_acquire+0x192/0x4070 kernel/locking/lockdep.c:3237
RSP: 0018:ffff88018b417380  EFLAGS: 00000002
RAX: ffffffff855b4ff0 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 1ffff1003ac3370e RSI: 0000000000000000 RDI: ffff8801d619b870
RBP: ffff88018b417530 R08: 0000000000000001 R09: 0000000000000000
R10: ffff880192f88000 R11: 0000000000000001 R12: 0000000000000001
R13: 0000000000000000 R14: ffff8801d619b868 R15: 0000000000000000
FS:  00007fac77894700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f83039ad000 CR3: 00000001bd0a7000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 0000000041b58ab3
c ffffffff843c1058
c ffffffff812343c0
c ffffffff81233857
c
 0000000000000000
c ffff880192f888c0
c 0000000600000007
c ffff880192f88000
c
 ffffffff839f5229
c ffff880192f888f0
c ffffffff855b4ff0
c 0000000000000001
c
Call Trace:
 [<ffffffff81238ea0>] lock_acquire+0x130/0x3e0 kernel/locking/lockdep.c:3756
 [<ffffffff839f3c56>] __raw_spin_lock include/linux/spinlock_api_smp.h:144 [inline]
 [<ffffffff839f3c56>] _raw_spin_lock+0x36/0x50 kernel/locking/spinlock.c:151
 [<ffffffff816215c6>] spin_lock include/linux/spinlock.h:302 [inline]
 [<ffffffff816215c6>] __find_get_block_slow+0xe6/0x330 fs/buffer.c:216
 [<ffffffff81621b4e>] __find_get_block+0x23e/0x4c0 fs/buffer.c:1360
 [<ffffffff81622959>] __getblk_slow fs/buffer.c:1101 [inline]
 [<ffffffff81622959>] __getblk_gfp+0x189/0x710 fs/buffer.c:1386
 [<ffffffff816262fd>] __bread_gfp+0x2d/0x270 fs/buffer.c:1420
 [<ffffffff818b4088>] sb_bread include/linux/buffer_head.h:300 [inline]
 [<ffffffff818b4088>] fat__get_entry+0x4c8/0x8f0 fs/fat/dir.c:100
 [<ffffffff818b6d11>] fat_get_entry fs/fat/dir.c:128 [inline]
 [<ffffffff818b6d11>] fat_get_short_entry+0x131/0x2a0 fs/fat/dir.c:876
 [<ffffffff818bec77>] fat_subdirs+0xc7/0x190 fs/fat/dir.c:942
 [<ffffffff818cef89>] fat_read_root fs/fat/inode.c:1402 [inline]
 [<ffffffff818cef89>] fat_fill_super+0x1cf9/0x3550 fs/fat/inode.c:1832
 [<ffffffff818d5d41>] vfat_fill_super+0x31/0x40 fs/fat/namei_vfat.c:1070
 [<ffffffff81579d67>] mount_bdev+0x2c7/0x390 fs/super.c:1100
 [<ffffffff818d5d04>] vfat_mount+0x34/0x40 fs/fat/namei_vfat.c:1077
 [<ffffffff8157baec>] mount_fs+0x28c/0x370 fs/super.c:1206
 [<ffffffff815db091>] vfs_kern_mount.part.29+0xd1/0x3d0 fs/namespace.c:991
 [<ffffffff815e29b9>] vfs_kern_mount fs/namespace.c:973 [inline]
 [<ffffffff815e29b9>] do_new_mount fs/namespace.c:2513 [inline]
 [<ffffffff815e29b9>] do_mount+0x3c9/0x2740 fs/namespace.c:2835
 [<ffffffff815e570e>] SYSC_mount fs/namespace.c:3051 [inline]
 [<ffffffff815e570e>] SyS_mount+0xfe/0x110 fs/namespace.c:3028
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f4893>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
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