Re: [PATCH] xfs: fix attr2 vs large data fork assert

[Christoph Hellwig <hch@infradead.org>]

ping?  This is a fairly nasty issue which should be fixed ASAP and go
into -stable.

On Fri, Nov 04, 2011 at 11:25:06AM -0400, Christoph Hellwig wrote:
> With Dmitry fsstress updates I've seen very reproducible crashes in
> xfs_attr_shortform_remove because xfs_attr_shortform_bytesfit claims that
> the attributes would not fit inline into the inode after removing an
> attribute.  It turns out that we were operating on an inode with lots
> of delalloc extents, and thus an if_bytes values for the data fork that
> is larger than biggest possible on-disk storage for it which utterly
> confuses the code near the end of xfs_attr_shortform_bytesfit.
> 
> Fix this by always allowing the current attribute fork, like we already
> do for the attr1 format, given that delalloc conversion will take care
> for moving either the data or attribute area out of line if it doesn't
> fit at that point - or making the point moot by merging extents at this
> point.
> 
> Also document the function better, and clean up some lose bits.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> Index: linux-2.6/fs/xfs/xfs_attr_leaf.c
> ===================================================================
> --- linux-2.6.orig/fs/xfs/xfs_attr_leaf.c	2011-11-04 13:46:59.481655134 +0100
> +++ linux-2.6/fs/xfs/xfs_attr_leaf.c	2011-11-04 15:58:06.480155275 +0100
> @@ -110,6 +110,7 @@ xfs_attr_namesp_match(int arg_flags, int
>  /*
>   * Query whether the requested number of additional bytes of extended
>   * attribute space will be able to fit inline.
> + *
>   * Returns zero if not, else the di_forkoff fork offset to be used in the
>   * literal area for attribute data once the new bytes have been added.
>   *
> @@ -136,11 +137,26 @@ xfs_attr_shortform_bytesfit(xfs_inode_t
>  		return (offset >= minforkoff) ? minforkoff : 0;
>  	}
>  
> -	if (!(mp->m_flags & XFS_MOUNT_ATTR2)) {
> -		if (bytes <= XFS_IFORK_ASIZE(dp))
> -			return dp->i_d.di_forkoff;
> +	/*
> +	 * If the requested numbers of bytes is smaller or equal to the
> +	 * current attribute fork size we can always proceed.
> +	 *
> +	 * Note that if_bytes in the data fork might actually be larger than
> +	 * the current data fork size is due to delalloc extents. In that
> +	 * case either the extent count will go down when they are converted
> +	 * to ral extents, or the delalloc conversion will take care of the
> +	 * literal area rebalancing.
> +	 */
> +	if (bytes <= XFS_IFORK_ASIZE(dp))
> +		return dp->i_d.di_forkoff;
> +
> +	/*
> +	 * For attr2 we can try to move the forkoff if there is space in the
> +	 * literal area, but for the old format we are done if there is no
> +	 * space in the fixes attribute fork.
> +	 */
> +	if (!(mp->m_flags & XFS_MOUNT_ATTR2))
>  		return 0;
> -	}
>  
>  	dsize = dp->i_df.if_bytes;
>  	
> @@ -157,10 +173,9 @@ xfs_attr_shortform_bytesfit(xfs_inode_t
>  		    xfs_default_attroffset(dp))
>  			dsize = XFS_BMDR_SPACE_CALC(MINDBTPTRS);
>  		break;
> -		
>  	case XFS_DINODE_FMT_BTREE:
>  		/*
> -		 * If have data btree then keep forkoff if we have one,
> +		 * If have a data btree then keep forkoff if we have one,
>  		 * otherwise we are adding a new attr, so then we set 
>  		 * minforkoff to where the btree root can finish so we have 
>  		 * plenty of room for attrs
> @@ -168,10 +183,9 @@ xfs_attr_shortform_bytesfit(xfs_inode_t
>  		if (dp->i_d.di_forkoff) {
>  			if (offset < dp->i_d.di_forkoff) 
>  				return 0;
> -			else 
> -				return dp->i_d.di_forkoff;
> -		} else
> -			dsize = XFS_BMAP_BROOT_SPACE(dp->i_df.if_broot);
> +			return dp->i_d.di_forkoff;
> +		}
> +		dsize = XFS_BMAP_BROOT_SPACE(dp->i_df.if_broot);
>  		break;
>  	}
>  	
> @@ -186,10 +200,10 @@ xfs_attr_shortform_bytesfit(xfs_inode_t
>  	maxforkoff = XFS_LITINO(mp) - XFS_BMDR_SPACE_CALC(MINABTPTRS);
>  	maxforkoff = maxforkoff >> 3;	/* rounded down */
>  
> -	if (offset >= minforkoff && offset < maxforkoff)
> -		return offset;
>  	if (offset >= maxforkoff)
>  		return maxforkoff;
> +	if (offset >= minforkoff)
> +		return offset;
>  	return 0;
>  }
>  
> 
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