Re: [PATCH V3 04/10] 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, hch@infradead.org
Subject: Re: [PATCH V3 04/10] xfs: Check for extent overflow when adding/removing xattrs
Date: Mon, 31 Aug 2020 09:37:59 -0700	[thread overview]
Message-ID: <20200831163759.GM6096@magnolia> (raw)
In-Reply-To: <20200820054349.5525-5-chandanrlinux@gmail.com>

On Thu, Aug 20, 2020 at 11:13:43AM +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>
> ---
>  fs/xfs/libxfs/xfs_attr.c       | 13 +++++++++++++
>  fs/xfs/libxfs/xfs_inode_fork.h |  9 +++++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> index d4583a0d1b3f..c481389da40f 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));

What happens if the free space is fragmented and each of these rmt
blocks results in a separate allocation?

I'm also not sure why we'd need to account for the remote blocks if
we're removing an attr?  Those mappings simply go away, right?

--D

> +		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 2642e4847ee0..aae8e6e80b71 100644
> --- a/fs/xfs/libxfs/xfs_inode_fork.h
> +++ b/fs/xfs/libxfs/xfs_inode_fork.h
> @@ -45,6 +45,15 @@ struct xfs_ifork {
>   * i.e. | Old extent | Hole | Old extent |
>   */
>  #define XFS_IEXT_REMOVE_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
> 