WARNING in unlock_new_inode

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
9dd2326890d89a5179967c947dab2bab34d7ddee (Fri Mar 30 17:29:47 2018 +0000)
Merge tag 'ceph-for-4.16-rc8' of git://github.com/ceph/ceph-client
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=187510916eb6a14598f7

So far this crash happened 4 times on upstream.
Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=6437140946747392
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=-2760467897697295172
compiler: gcc (GCC) 7.1.1 20170620

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Reported-by: syzbot+187510916eb6a14598f7@xxxxxxxxxxxxxxxxxxxxxxxxx
It will help syzbot understand when the bug is fixed. See footer for  
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hfs: can't find a HFS filesystem on dev loop3
FAT-fs (loop3): invalid media value (0xd8)
FAT-fs (loop3): Can't find a valid FAT filesystem
REISERFS (device loop2): Using r5 hash to sort names
REISERFS (device loop2): using 3.5.x disk format
WARNING: CPU: 1 PID: 21970 at fs/inode.c:958 unlock_new_inode+0xea/0x120  
fs/inode.c:958
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 21970 Comm: syz-executor2 Not tainted 4.16.0-rc7+ #7
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x24d lib/dump_stack.c:53
 panic+0x1e4/0x41c kernel/panic.c:183
 __warn+0x1dc/0x200 kernel/panic.c:547
 report_bug+0x1f4/0x2b0 lib/bug.c:186
 fixup_bug.part.10+0x37/0x80 arch/x86/kernel/traps.c:178
 fixup_bug arch/x86/kernel/traps.c:247 [inline]
 do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
 invalid_op+0x1b/0x40 arch/x86/entry/entry_64.S:986
RIP: 0010:unlock_new_inode+0xea/0x120 fs/inode.c:958
RSP: 0018:ffff8801ad387120 EFLAGS: 00010246
RAX: 0000000000040000 RBX: ffff88017ecfe1a8 RCX: ffffffff81b7f52a
RDX: 0000000000040000 RSI: ffffc900036cc000 RDI: ffff88017ecfe234
RBP: ffff8801ad387140 R08: 1ffff10035a70d63 R09: 0000000000000004
R10: ffff8801ad386fd8 R11: 0000000000000007 R12: 0000000000000000
R13: ffff88017ecfe280 R14: ffff88017ecfe230 R15: ffff8801ad387598
 reiserfs_new_inode+0x616/0x32a0 fs/reiserfs/inode.c:2159
 reiserfs_mkdir+0x418/0x840 fs/reiserfs/namei.c:840
 xattr_mkdir.constprop.14+0x115/0x170 fs/reiserfs/xattr.c:76
 create_privroot fs/reiserfs/xattr.c:857 [inline]
 reiserfs_xattr_init+0x501/0x970 fs/reiserfs/xattr.c:976
 reiserfs_fill_super+0x2b26/0x33a0 fs/reiserfs/super.c:2176
 mount_bdev+0x2b7/0x370 fs/super.c:1119
 get_super_block+0x34/0x40 fs/reiserfs/super.c:2605
 mount_fs+0x66/0x2d0 fs/super.c:1222
 vfs_kern_mount.part.26+0xc6/0x4a0 fs/namespace.c:1037
 vfs_kern_mount fs/namespace.c:2509 [inline]
 do_new_mount fs/namespace.c:2512 [inline]
 do_mount+0xea4/0x2bb0 fs/namespace.c:2842
 SYSC_mount fs/namespace.c:3058 [inline]
 SyS_mount+0xab/0x120 fs/namespace.c:3035
 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4578aa
RSP: 002b:00007f3983b39bb8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000020000000 RCX: 00000000004578aa
RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007f3983b39c00
RBP: 0000000000000007 R08: 0000000020011500 R09: 0000000020000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000013
R13: 000000000000066d R14: 00000000006fbad8 R15: 0000000000000000
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


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