Re: [PATCH] xfs: ignore leaf attr ichdr.count in verifier during log replay

[Brian Foster <bfoster@redhat.com>]

On Wed, Nov 30, 2016 at 04:33:15PM -0600, Eric Sandeen wrote:
> When we create a new attribute, we first create a shortform
> attribute, and try to fit the new attribute into it.
> If that fails, we copy the (empty) attribute into a leaf attribute,
> and do the copy again.  Thus there can be a transient state where
> we have an empty leaf attribute.
> 
> If we encounter this during log replay, the verifier will fail.
> So add a test to ignore this part of the leaf attr verification
> during log replay.
> 
> Thanks as usual to dchinner for spotting the problem.
> 
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
> 
> diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
> index 8ea91f3..2852521 100644
> --- a/fs/xfs/libxfs/xfs_attr_leaf.c
> +++ b/fs/xfs/libxfs/xfs_attr_leaf.c
> @@ -253,6 +253,7 @@ STATIC void xfs_attr3_leaf_moveents(struct xfs_da_args *args,
>  {
>  	struct xfs_mount	*mp = bp->b_target->bt_mount;
>  	struct xfs_attr_leafblock *leaf = bp->b_addr;
> +	struct xfs_perag *pag = bp->b_pag;
>  	struct xfs_attr3_icleaf_hdr ichdr;
>  
>  	xfs_attr3_leaf_hdr_from_disk(mp->m_attr_geo, &ichdr, leaf);
> @@ -273,7 +274,12 @@ STATIC void xfs_attr3_leaf_moveents(struct xfs_da_args *args,
>  		if (ichdr.magic != XFS_ATTR_LEAF_MAGIC)
>  			return false;
>  	}
> -	if (ichdr.count == 0)
> +	/*
> +	 * In recovery there is a transient state where count == 0 is valid
> +	 * because we may have transitioned an empty shortform attr to a leaf
> +	 * if the attr didn't fit in shortform.
> +	 */
> +	if (pag && pag->pagf_init && ichdr.count == 0)
>  		return false;

Seems fine, but if the idea is to filter out failures during log
recovery, can we detect that state explicitly? E.g., check for some
combination of XLOG_ACTIVE_RECOVERY and/or XLOG_RECOVERY_NEEDED (or just
define and use a new flag/helper if necessary)?

Brian

>  
>  	/* XXX: need to range check rest of attr header values */
> --
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