Re: [PATCH] xfs: fix missing ILOCK unlock when xfs_setattr_nonsize fails due to EDQUOT

[Dave Chinner <david@fromorbit.com>]

On Thu, Aug 22, 2019 at 08:55:28PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Benjamin Moody reported to Debian that XFS partially wedges when a chgrp
> fails on account of being out of disk quota.  I ran his reproducer
> script:
> 
> # adduser dummy
> # adduser dummy plugdev
> 
> # dd if=/dev/zero bs=1M count=100 of=test.img
> # mkfs.xfs test.img
> # mount -t xfs -o gquota test.img /mnt
> # mkdir -p /mnt/dummy
> # chown -c dummy /mnt/dummy
> # xfs_quota -xc 'limit -g bsoft=100k bhard=100k plugdev' /mnt
> 
> (and then as user dummy)
> 
> $ dd if=/dev/urandom bs=1M count=50 of=/mnt/dummy/foo
> $ chgrp plugdev /mnt/dummy/foo
> 
> and saw:
> 
> ================================================
> WARNING: lock held when returning to user space!
> 5.3.0-rc5 #rc5 Tainted: G        W
> ------------------------------------------------
> chgrp/47006 is leaving the kernel with locks still held!
> 1 lock held by chgrp/47006:
>  #0: 000000006664ea2d (&xfs_nondir_ilock_class){++++}, at: xfs_ilock+0xd2/0x290 [xfs]
> 
> ...which is clearly caused by xfs_setattr_nonsize failing to unlock the
> ILOCK after the xfs_qm_vop_chown_reserve call fails.  Add the missing
> unlock.
> 
> Reported-by: benjamin.moody@gmail.com
> Fixes: 253f4911f297 ("xfs: better xfs_trans_alloc interface")
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/xfs/xfs_iops.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index dd4076ae228a..ea614b4ae052 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -804,6 +804,7 @@ xfs_setattr_nonsize(
>  
>  out_cancel:
>  	xfs_trans_cancel(tp);
> +	xfs_iunlock(ip, XFS_ILOCK_EXCL);
>  out_dqrele:
>  	xfs_qm_dqrele(udqp);
>  	xfs_qm_dqrele(gdqp);

/me goes back an looks at 253f4911f297 ("xfs: better xfs_trans_alloc
interface")

Fmeh. The original patch posting did:

out_unlock:
 	xfs_iunlock(ip, XFS_ILOCK_EXCL);
-out_trans_cancel:
-	xfs_trans_cancel(tp);
+out_dqrele:
 	xfs_qm_dqrele(udqp);
 	xfs_qm_dqrele(gdqp);
 	return error;

Which leaked the transaction. Looks like I screwed up fixing that
up on commit - it no longer leaked the transaction, but leaked the
lock instead. And 3 and half years later someone notices it...

Oh, gawd that code is so grotty! I started saying "maybe we
should..." and then stopped when I realised just how much cleanup
needs to be done to that function...

The above patch fixes the issue, iso consider it:

Reviewed-by: Dave Chinner <dchinner@redhat.com>

-- 
Dave Chinner
david@fromorbit.com