Re: [PATCH V11 04/14] xfs: Check for extent overflow when adding/removing xattrs

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Tue, Nov 17, 2020 at 07:14:06PM +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.
> 
> To be able to always remove an existing xattr, when adding an xattr we
> make sure to reserve inode fork extent count required for removing max
> sized xattr in addition to that required by the xattr add operation.
> 
> Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
> ---
>  fs/xfs/libxfs/xfs_attr.c       | 20 ++++++++++++++++++++
>  fs/xfs/libxfs/xfs_inode_fork.h | 10 ++++++++++
>  2 files changed, 30 insertions(+)
> 
> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> index fd8e6418a0d3..d53b3867b308 100644
> --- a/fs/xfs/libxfs/xfs_attr.c
> +++ b/fs/xfs/libxfs/xfs_attr.c
> @@ -396,6 +396,8 @@ xfs_attr_set(
>  	struct xfs_trans_res	tres;
>  	bool			rsvd = (args->attr_filter & XFS_ATTR_ROOT);
>  	int			error, local;
> +	int			iext_cnt;
> +	int			rmt_blks;
>  	unsigned int		total;
>  
>  	if (XFS_FORCED_SHUTDOWN(dp->i_mount))
> @@ -416,6 +418,9 @@ xfs_attr_set(
>  	 */
>  	args->op_flags = XFS_DA_OP_OKNOENT;
>  
> +	rmt_blks = xfs_attr3_rmt_blocks(mp, XFS_XATTR_SIZE_MAX);
> +	iext_cnt = XFS_IEXT_ATTR_MANIP_CNT(rmt_blks);

These values are only relevant for the xattr removal case, right?
AFAICT the args->value != NULL case immediately after will set new
values, so why not just move this into...

> +
>  	if (args->value) {
>  		XFS_STATS_INC(mp, xs_attr_set);
>  
> @@ -442,6 +447,13 @@ 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 = 0;
> +		else
> +			rmt_blks = xfs_attr3_rmt_blocks(mp, args->valuelen);
> +
> +		iext_cnt += XFS_IEXT_ATTR_MANIP_CNT(rmt_blks);
>  	} else {
>  		XFS_STATS_INC(mp, xs_attr_remove);

...the bottom of this clause here.

>  
> @@ -460,6 +472,14 @@ xfs_attr_set(
>  
>  	xfs_ilock(dp, XFS_ILOCK_EXCL);
>  	xfs_trans_ijoin(args->trans, dp, 0);
> +
> +	if (args->value || xfs_inode_hasattr(dp)) {

Can this simply be "if (iext_cnt != 0)" ?

--D

> +		error = xfs_iext_count_may_overflow(dp, XFS_ATTR_FORK,
> +				iext_cnt);
> +		if (error)
> +			goto out_trans_cancel;
> +	}
> +
>  	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
>