kernel BUG at fs/btrfs/volumes.c:LINE!

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    af6c5d5e01ad Merge branch 'for-4.18' of git://git.kernel.o..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15f700af800000
kernel config:  https://syzkaller.appspot.com/x/.config?x=12ff770540994680
dashboard link: https://syzkaller.appspot.com/bug?extid=5b658d997a83984507a6
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+5b658d997a83984507a6@xxxxxxxxxxxxxxxxxxxxxxxxx

RDX: 0000000020000080 RSI: 0000000020000040 RDI: 00007f787067fbf0
RBP: 0000000000000001 R08: 00000000200000c0 R09: 0000000020000080
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000014
R13: 0000000000000001 R14: 0000000000700008 R15: 0000000000000043
------------[ cut here ]------------
kernel BUG at fs/btrfs/volumes.c:1032!
invalid opcode: 0000 [#1] SMP KASAN
CPU: 1 PID: 22303 Comm: syz-executor1 Not tainted 4.17.0+ #86
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:btrfs_prepare_close_one_device fs/btrfs/volumes.c:1032 [inline]
RIP: 0010:close_fs_devices+0xba7/0xfa0 fs/btrfs/volumes.c:1052
Code: 56 18 48 89 f8 48 c1 e8 03 80 3c 18 00 0f 85 2b 03 00 00 49 83 6c 24  
30 01 e9 25 f8 ff ff e8 90 f4 b3 fe 0f 0b e8 89 f4 b3 fe <0f> 0b 48 89 f7  
e8 ef 64 f0 fe e9 f6 f5 ff ff e8 75 f4 b3 fe 0f 0b
RSP: 0018:ffff8801af6ff050 EFLAGS: 00010246
RAX: 0000000000040000 RBX: dffffc0000000000 RCX: ffffc9000c70c000
RDX: 0000000000040000 RSI: ffffffff82c56437 RDI: 0000000000000286
RBP: ffff8801af6ff350 R08: ffffed003b5e46d7 R09: ffffed003b5e46d6
R10: ffffed003b5e46d6 R11: ffff8801daf236b3 R12: ffff8801c58ac190
R13: 0000000000000000 R14: ffff8801b1a6a940 R15: ffff8801b4d7d680
FS:  00007f7870680700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000704094 CR3: 00000001c51e8000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 btrfs_close_devices+0x29/0x150 fs/btrfs/volumes.c:1085
 btrfs_mount_root+0x1419/0x1e70 fs/btrfs/super.c:1610
 mount_fs+0xae/0x328 fs/super.c:1277
 vfs_kern_mount.part.34+0xd4/0x4d0 fs/namespace.c:1037
 vfs_kern_mount+0x40/0x60 fs/namespace.c:1027
 btrfs_mount+0x4a1/0x213e fs/btrfs/super.c:1661
 mount_fs+0xae/0x328 fs/super.c:1277
 vfs_kern_mount.part.34+0xd4/0x4d0 fs/namespace.c:1037
 vfs_kern_mount fs/namespace.c:1027 [inline]
 do_new_mount fs/namespace.c:2518 [inline]
 do_mount+0x564/0x30b0 fs/namespace.c:2848
 ksys_mount+0x12d/0x140 fs/namespace.c:3064
 __do_sys_mount fs/namespace.c:3078 [inline]
 __se_sys_mount fs/namespace.c:3075 [inline]
 __x64_sys_mount+0xbe/0x150 fs/namespace.c:3075
 do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45843a
Code: b8 a6 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 dd 8f fb ff c3 66 2e 0f  
1f 84 00 00 00 00 00 66 90 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 ba 8f fb ff c3 66 0f 1f 84 00 00 00 00 00
RSP: 002b:00007f787067fba8 EFLAGS: 00000202 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000020000080 RCX: 000000000045843a
RDX: 0000000020000080 RSI: 0000000020000040 RDI: 00007f787067fbf0
RBP: 0000000000000001 R08: 00000000200000c0 R09: 0000000020000080
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000014
R13: 0000000000000001 R14: 0000000000700008 R15: 0000000000000043
Modules linked in:
Dumping ftrace buffer:
   (ftrace buffer empty)
---[ end trace 383b0406a01f2edd ]---
RIP: 0010:btrfs_prepare_close_one_device fs/btrfs/volumes.c:1032 [inline]
RIP: 0010:close_fs_devices+0xba7/0xfa0 fs/btrfs/volumes.c:1052
Code: 56 18 48 89 f8 48 c1 e8 03 80 3c 18 00 0f 85 2b 03 00 00 49 83 6c 24  
30 01 e9 25 f8 ff ff e8 90 f4 b3 fe 0f 0b e8 89 f4 b3 fe <0f> 0b 48 89 f7  
e8 ef 64 f0 fe e9 f6 f5 ff ff e8 75 f4 b3 fe 0f 0b
RSP: 0018:ffff8801af6ff050 EFLAGS: 00010246
RAX: 0000000000040000 RBX: dffffc0000000000 RCX: ffffc9000c70c000
RDX: 0000000000040000 RSI: ffffffff82c56437 RDI: 0000000000000286
RBP: ffff8801af6ff350 R08: ffffed003b5e46d7 R09: ffffed003b5e46d6
R10: ffffed003b5e46d6 R11: ffff8801daf236b3 R12: ffff8801c58ac190
R13: 0000000000000000 R14: ffff8801b1a6a940 R15: ffff8801b4d7d680
FS:  00007f7870680700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000704094 CR3: 00000001c51e8000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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