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SubjectWARNING: bad unlock balance in xfs_iunlock

syzbot hit the following crash on upstream commit
86bbbebac1933e6e95e8234c4f7d220c5ddd38bc (Mon Apr 2 18:47:07 2018 +0000)
Merge branch 'ras-core-for-linus' of
syzbot dashboard link:

C reproducer:
syzkaller reproducer:
Raw console output:
Kernel config:
compiler: gcc (GCC) 7.1.1 20170620

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000000005e445429: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 ................
00000000c1c426da: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 ................
XFS (loop0): metadata I/O error in "xfs_trans_read_buf_map" at daddr 0x1
len 1 error 117

WARNING: bad unlock balance detected!
4.16.0+ #11 Not tainted
syzkaller109734/4463 is trying to release lock (&xfs_nondir_ilock_class) at:
[<ffffffff8276589f>] mrunlock_excl fs/xfs/mrlock.h:74 [inline]
[<ffffffff8276589f>] xfs_iunlock+0x36f/0x4a0 fs/xfs/xfs_inode.c:329
but there are no more locks to release!

other info that might help us debug this:
2 locks held by syzkaller109734/4463:
#0: 00000000b4cfce0b (&type->s_umount_key#36/1){+.+.}, at: alloc_super
fs/super.c:211 [inline]
#0: 00000000b4cfce0b (&type->s_umount_key#36/1){+.+.}, at:
sget_userns+0x3b2/0xe60 fs/super.c:502
#1: 00000000d8e8aeed (sb_internal#2){.+.+}, at: sb_start_intwrite
include/linux/fs.h:1595 [inline]
#1: 00000000d8e8aeed (sb_internal#2){.+.+}, at:
xfs_trans_alloc+0x349/0x430 fs/xfs/xfs_trans.c:264

stack backtrace:
CPU: 1 PID: 4463 Comm: syzkaller109734 Not tainted 4.16.0+ #11
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+0x1a7/0x27d lib/dump_stack.c:53
print_unlock_imbalance_bug+0x12f/0x140 kernel/locking/lockdep.c:3484
__lock_release kernel/locking/lockdep.c:3691 [inline]
lock_release+0x6fe/0xa40 kernel/locking/lockdep.c:3939
up_write+0x72/0x210 kernel/locking/rwsem.c:132
mrunlock_excl fs/xfs/mrlock.h:74 [inline]
xfs_iunlock+0x36f/0x4a0 fs/xfs/xfs_inode.c:329
xfs_inode_item_unlock+0x82/0xa0 fs/xfs/xfs_inode_item.c:600
xfs_trans_free_items+0x176/0x230 fs/xfs/xfs_trans.c:790
xfs_trans_cancel+0x1bb/0x260 fs/xfs/xfs_trans.c:1047
xfs_qm_dqread+0xc7c/0x13b0 fs/xfs/xfs_dquot.c:623
xfs_qm_dqget+0x6b9/0x2060 fs/xfs/xfs_dquot.c:766
xfs_qm_quotacheck_dqadjust+0xe4/0x800 fs/xfs/xfs_qm.c:1080
xfs_qm_dqusage_adjust+0x814/0x11c0 fs/xfs/xfs_qm.c:1194
xfs_bulkstat_ag_ichunk fs/xfs/xfs_itable.c:302 [inline]
xfs_bulkstat+0xc0a/0x1cb0 fs/xfs/xfs_itable.c:487
xfs_qm_quotacheck+0x3cb/0x800 fs/xfs/xfs_qm.c:1340
xfs_qm_mount_quotas+0x2c4/0x470 fs/xfs/xfs_qm.c:1459
xfs_mountfs+0x22a1/0x2690 fs/xfs/xfs_mount.c:982
xfs_fs_fill_super+0xc8d/0x1250 fs/xfs/xfs_super.c:1703
mount_bdev+0x2b7/0x370 fs/super.c:1119
xfs_fs_mount+0x34/0x40 fs/xfs/xfs_super.c:1770
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
RIP: 0033:0x44488a
RSP: 002b:00007fff118ea198 EFLAGS: 00000202 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda R

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