Re: [PATCH V5 04/12] xfs: Check for extent overflow when adding/removing xattrs

From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Chandan Babu R <chandanrlinux@gmail.com>
Cc: linux-xfs@vger.kernel.org, david@fromorbit.com
Subject: Re: [PATCH V5 04/12] xfs: Check for extent overflow when adding/removing xattrs
Date: Mon, 5 Oct 2020 21:23:29 -0700	[thread overview]
Message-ID: <20201006042329.GN49547@magnolia> (raw)
In-Reply-To: <20201003055633.9379-5-chandanrlinux@gmail.com>

On Sat, Oct 03, 2020 at 11:26:25AM +0530, Chandan Babu R wrote:
> Adding/removing an xattr can cause XFS_DA_NODE_MAXDEPTH extents to be
> added. One extra extent for dabtree in case a local attr is large enough
> to cause a double split.  It can also cause extent count to increase
> proportional to the size of a remote xattr's value.
> 
> Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>

Didn't I already review this?  AFAICT it hasn't changed much, but did
something change enough to warrant dropping the old RVB tag?

> ---
>  fs/xfs/libxfs/xfs_attr.c       | 13 +++++++++++++
>  fs/xfs/libxfs/xfs_inode_fork.h | 10 ++++++++++
>  2 files changed, 23 insertions(+)
> 
> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> index fd8e6418a0d3..be51e7068dcd 100644
> --- a/fs/xfs/libxfs/xfs_attr.c
> +++ b/fs/xfs/libxfs/xfs_attr.c
> @@ -396,6 +396,7 @@ xfs_attr_set(
>  	struct xfs_trans_res	tres;
>  	bool			rsvd = (args->attr_filter & XFS_ATTR_ROOT);
>  	int			error, local;
> +	int			rmt_blks = 0;
>  	unsigned int		total;
>  
>  	if (XFS_FORCED_SHUTDOWN(dp->i_mount))
> @@ -442,11 +443,15 @@ xfs_attr_set(
>  		tres.tr_logcount = XFS_ATTRSET_LOG_COUNT;
>  		tres.tr_logflags = XFS_TRANS_PERM_LOG_RES;
>  		total = args->total;
> +
> +		if (!local)
> +			rmt_blks = xfs_attr3_rmt_blocks(mp, args->valuelen);
>  	} else {
>  		XFS_STATS_INC(mp, xs_attr_remove);
>  
>  		tres = M_RES(mp)->tr_attrrm;
>  		total = XFS_ATTRRM_SPACE_RES(mp);
> +		rmt_blks = xfs_attr3_rmt_blocks(mp, XFS_XATTR_SIZE_MAX);
>  	}
>  
>  	/*
> @@ -460,6 +465,14 @@ xfs_attr_set(
>  
>  	xfs_ilock(dp, XFS_ILOCK_EXCL);
>  	xfs_trans_ijoin(args->trans, dp, 0);
> +
> +	if (args->value || xfs_inode_hasattr(dp)) {
> +		error = xfs_iext_count_may_overflow(dp, XFS_ATTR_FORK,
> +				XFS_IEXT_ATTR_MANIP_CNT(rmt_blks));
> +		if (error)
> +			goto out_trans_cancel;

Hmm.  If you hit this while trying to remove an xattr, what then?
I suppose you really don't want to overflow naextents, but I suppose the
only other option is to delete the file.  Oh well, attr forks with 65533
extents should be vanishingly rare, right?  Right? :)

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> +	}
> +
>  	if (args->value) {
>  		unsigned int	quota_flags = XFS_QMOPT_RES_REGBLKS;
>  
> diff --git a/fs/xfs/libxfs/xfs_inode_fork.h b/fs/xfs/libxfs/xfs_inode_fork.h
> index bcac769a7df6..5de2f07d0dd5 100644
> --- a/fs/xfs/libxfs/xfs_inode_fork.h
> +++ b/fs/xfs/libxfs/xfs_inode_fork.h
> @@ -47,6 +47,16 @@ struct xfs_ifork {
>   */
>  #define XFS_IEXT_PUNCH_HOLE_CNT		(1)
>  
> +/*
> + * Adding/removing an xattr can cause XFS_DA_NODE_MAXDEPTH extents to
> + * be added. One extra extent for dabtree in case a local attr is
> + * large enough to cause a double split.  It can also cause extent
> + * count to increase proportional to the size of a remote xattr's
> + * value.
> + */
> +#define XFS_IEXT_ATTR_MANIP_CNT(rmt_blks) \
> +	(XFS_DA_NODE_MAXDEPTH + max(1, rmt_blks))
> +
>  /*
>   * Fork handling.
>   */
> -- 
> 2.28.0
> 