Re: [PATCH 03/10] xfs_repair: correctly account for free space btree shrinks when fixing freelist

[Bill O'Donnell <billodo@redhat.com>]

On Mon, Apr 22, 2019 at 08:45:09AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> When we fix the freelist at the end of build_agf_agfl in phase 5 of
> repair, we need to create incore rmap records for the blocks that get
> added to the AGFL.  We can't let the regular freelist fixing code use
> the regular on-disk rmapbt update code because the rmapbt isn't fully
> set up yet.
> 
> Unfortunately, the original code fails to account for the fact that the
> free space btrees can shrink when we allocate blocks to fix the
> freelist; those blocks are also put on the freelist, but there are
> already incore rmaps for all the free space btree blocks.  We must not
> create (redundant) incore rmaps for those blocks.  If we do, repair
> fails with a complaint that rebuilding the rmapbt failed during phase 5.
> xfs/137 on a 1k block size occasionally triggers this bug.
> 
> To fix the problem, construct a bitmap of all OWN_AG blocks that we know
> about before traversing the AGFL, and only create new incore rmaps for
> those AGFL blocks that are not already tracked in the bitmap.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

looks good to me.
Reviewed-by: Bill O'Donnell <billodo@redhat.com>

> ---
>  repair/rmap.c |   54 ++++++++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 44 insertions(+), 10 deletions(-)
> 
> 
> diff --git a/repair/rmap.c b/repair/rmap.c
> index d0156f9d..19cceca3 100644
> --- a/repair/rmap.c
> +++ b/repair/rmap.c
> @@ -12,6 +12,7 @@
>  #include "dinode.h"
>  #include "slab.h"
>  #include "rmap.h"
> +#include "bitmap.h"
>  
>  #undef RMAP_DEBUG
>  
> @@ -450,15 +451,16 @@ rmap_store_ag_btree_rec(
>  	struct xfs_buf		*agflbp = NULL;
>  	struct xfs_trans	*tp;
>  	__be32			*agfl_bno, *b;
> +	struct xfs_ag_rmap	*ag_rmap = &ag_rmaps[agno];
> +	struct bitmap		*own_ag_bitmap = NULL;
>  	int			error = 0;
>  
>  	if (!xfs_sb_version_hasrmapbt(&mp->m_sb))
>  		return 0;
>  
>  	/* Release the ar_rmaps; they were put into the rmapbt during p5. */
> -	free_slab(&ag_rmaps[agno].ar_rmaps);
> -	error = init_slab(&ag_rmaps[agno].ar_rmaps,
> -				  sizeof(struct xfs_rmap_irec));
> +	free_slab(&ag_rmap->ar_rmaps);
> +	error = init_slab(&ag_rmap->ar_rmaps, sizeof(struct xfs_rmap_irec));
>  	if (error)
>  		goto err;
>  
> @@ -478,19 +480,50 @@ rmap_store_ag_btree_rec(
>  	 * rmap, we only need to add rmap records for AGFL blocks past
>  	 * that point in the AGFL because those blocks are a result of a
>  	 * no-rmap no-shrink freelist fixup that we did earlier.
> +	 *
> +	 * However, some blocks end up on the AGFL because the free space
> +	 * btrees shed blocks as a result of allocating space to fix the
> +	 * freelist.  We already created in-core rmap records for the free
> +	 * space btree blocks, so we must be careful not to create those
> +	 * records again.  Create a bitmap of already-recorded OWN_AG rmaps.
>  	 */
> +	error = init_slab_cursor(ag_rmap->ar_raw_rmaps, rmap_compare, &rm_cur);
> +	if (error)
> +		goto err;
> +	if (!bitmap_init(&own_ag_bitmap)) {
> +		error = -ENOMEM;
> +		goto err_slab;
> +	}
> +	while ((rm_rec = pop_slab_cursor(rm_cur)) != NULL) {
> +		if (rm_rec->rm_owner != XFS_RMAP_OWN_AG)
> +			continue;
> +		if (!bitmap_set(own_ag_bitmap, rm_rec->rm_startblock,
> +					rm_rec->rm_blockcount)) {
> +			error = EFSCORRUPTED;
> +			goto err_slab;
> +		}
> +	}
> +	free_slab_cursor(&rm_cur);
> +
> +	/* Create rmaps for any AGFL blocks that aren't already rmapped. */
>  	agfl_bno = XFS_BUF_TO_AGFL_BNO(mp, agflbp);
> -	b = agfl_bno + ag_rmaps[agno].ar_flcount;
> +	b = agfl_bno + ag_rmap->ar_flcount;
>  	while (*b != cpu_to_be32(NULLAGBLOCK) &&
>  	       b - agfl_bno < libxfs_agfl_size(mp)) {
> -		error = rmap_add_ag_rec(mp, agno, be32_to_cpu(*b), 1,
> -				XFS_RMAP_OWN_AG);
> -		if (error)
> -			goto err;
> +		xfs_agblock_t	agbno;
> +
> +		agbno = be32_to_cpu(*b);
> +		if (!bitmap_test(own_ag_bitmap, agbno, 1)) {
> +			error = rmap_add_ag_rec(mp, agno, agbno, 1,
> +					XFS_RMAP_OWN_AG);
> +			if (error)
> +				goto err;
> +		}
>  		b++;
>  	}
>  	libxfs_putbuf(agflbp);
>  	agflbp = NULL;
> +	bitmap_free(&own_ag_bitmap);
>  
>  	/* Merge all the raw rmaps into the main list */
>  	error = rmap_fold_raw_recs(mp, agno);
> @@ -498,8 +531,7 @@ rmap_store_ag_btree_rec(
>  		goto err;
>  
>  	/* Create cursors to refcount structures */
> -	error = init_slab_cursor(ag_rmaps[agno].ar_rmaps, rmap_compare,
> -			&rm_cur);
> +	error = init_slab_cursor(ag_rmap->ar_rmaps, rmap_compare, &rm_cur);
>  	if (error)
>  		goto err;
>  
> @@ -542,6 +574,8 @@ rmap_store_ag_btree_rec(
>  err:
>  	if (agflbp)
>  		libxfs_putbuf(agflbp);
> +	if (own_ag_bitmap)
> +		bitmap_free(&own_ag_bitmap);
>  	return error;
>  }
>  
>