[PATCH 3/6] xfs: bulkstat chunk-formatter has issues

[Brian Foster]

On Tue, Nov 04, 2014 at 11:53:18PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner at redhat.com>
> 
> The loop construct has issues:
> 	- clustidx is completely unused, so remove it.
> 	- the loop tries to be smart by terminating when the
> 	  "freecount" tells it that all inodes are free. Just drop
> 	  it as in most cases we have to scan all inodes in the
> 	  chunk anyway.
> 	- move the "user buffer left" condition check to the only
> 	  point where we consume space int eh user buffer.
> 	- move the initialisation of agino out of the loop, leaving
> 	  just a simple loop control logic using the clusteridx.
> 
> Also, double handling of the user buffer variables leads to problems
> tracking the current state - use the cursor variables directly
> rather than keeping local copies and then having to update the
> cursor before returning.
> 
> cc: <stable at vger.kernel.org>
> Signed-off-by: Dave Chinner <dchinner at redhat.com>
> ---
>  fs/xfs/xfs_itable.c | 55 ++++++++++++++++++++---------------------------------
>  1 file changed, 21 insertions(+), 34 deletions(-)
> 
> diff --git a/fs/xfs/xfs_itable.c b/fs/xfs/xfs_itable.c
> index 50a3e59..ff31965 100644
> --- a/fs/xfs/xfs_itable.c
> +++ b/fs/xfs/xfs_itable.c
> @@ -283,59 +283,46 @@ xfs_bulkstat_ag_ichunk(
>  	xfs_ino_t			*lastino)
>  {
>  	char				__user **ubufp = acp->ac_ubuffer;
> -	int				ubleft = acp->ac_ubleft;
> -	int				ubelem = acp->ac_ubelem;
> -	int				chunkidx, clustidx;
> +	int				chunkidx;
>  	int				error = 0;
>  	xfs_agino_t			agino;
>  
> -	for (agino = irbp->ir_startino, chunkidx = clustidx = 0;
> -	     XFS_BULKSTAT_UBLEFT(ubleft) &&
> -	     irbp->ir_freecount < XFS_INODES_PER_CHUNK;
> -	     chunkidx++, clustidx++, agino++) {
> -		int		fmterror;	/* bulkstat formatter result */
> +	agino = irbp->ir_startino;
> +	for (chunkidx = 0; chunkidx < XFS_INODES_PER_CHUNK;
> +	     chunkidx++, agino++) {
> +		int		fmterror;
>  		int		ubused;
>  		xfs_ino_t	ino = XFS_AGINO_TO_INO(mp, agno, agino);
>  
> -		ASSERT(chunkidx < XFS_INODES_PER_CHUNK);
> -
>  		/* Skip if this inode is free */
>  		if (XFS_INOBT_MASK(chunkidx) & irbp->ir_free) {
>  			*lastino = ino;
>  			continue;
>  		}
>  
> -		/*
> -		 * Count used inodes as free so we can tell when the
> -		 * chunk is used up.
> -		 */
> -		irbp->ir_freecount++;
> -
>  		/* Get the inode and fill in a single buffer */
>  		ubused = statstruct_size;
> -		error = formatter(mp, ino, *ubufp, ubleft, &ubused, &fmterror);
> -		if (fmterror == BULKSTAT_RV_NOTHING) {
> -			if (error && error != -ENOENT && error != -EINVAL) {
> -				ubleft = 0;
> -				break;
> -			}
> -			*lastino = ino;
> -			continue;
> -		}
> -		if (fmterror == BULKSTAT_RV_GIVEUP) {
> -			ubleft = 0;
> +		error = formatter(mp, ino, *ubufp, acp->ac_ubleft,
> +				  &ubused, &fmterror);
> +		if (fmterror == BULKSTAT_RV_GIVEUP ||
> +		    (error && error != -ENOENT && error != -EINVAL)) {
> +			acp->ac_ubleft = 0;
>  			ASSERT(error);
>  			break;
>  		}
> -		if (*ubufp)
> -			*ubufp += ubused;
> -		ubleft -= ubused;
> -		ubelem++;
> +		if (fmterror == BULKSTAT_RV_NOTHING || error) {
> +			*lastino = ino;
> +			continue;
> +		}

Not introduced by this patch, but this looks like inconsistent error
handling. The structure of the code suggests we intend to carry on in
the event of ENOENT or EINVAL, but said errors can leak out of this
function if we never get back to the formatter call (e.g., we're at the
last inode or all subsequent inodes are free).

Brian

> +
> +		*ubufp += ubused;
> +		acp->ac_ubleft -= ubused;
> +		acp->ac_ubelem++;
>  		*lastino = ino;
> -	}
>  
> -	acp->ac_ubleft = ubleft;
> -	acp->ac_ubelem = ubelem;
> +		if (acp->ac_ubleft < statstruct_size)
> +			break;
> +	}
>  
>  	return error;
>  }
> -- 
> 2.0.0
> 
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