On Fri, Jun 21, 2024 at 10:05:33AM +0000, John Garry wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> If args->minlen is not aligned to the constraints of forced
> alignment, we may do minlen allocations that are not aligned when we
> approach ENOSPC. Avoid this by always aligning args->minlen
> appropriately. If alignment of minlen results in a value smaller
> than the alignment constraint, fail the allocation immediately.
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
Looks good!
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
--D
> ---
> fs/xfs/libxfs/xfs_bmap.c | 45 +++++++++++++++++++++++++++-------------
> 1 file changed, 31 insertions(+), 14 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 9131ba8113a6..c9cf138e13c4 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -3278,33 +3278,48 @@ xfs_bmap_longest_free_extent(
> return 0;
> }
>
> -static xfs_extlen_t
> +static int
> xfs_bmap_select_minlen(
> struct xfs_bmalloca *ap,
> struct xfs_alloc_arg *args,
> xfs_extlen_t blen)
> {
> -
> /* Adjust best length for extent start alignment. */
> if (blen > args->alignment)
> blen -= args->alignment;
>
> /*
> * Since we used XFS_ALLOC_FLAG_TRYLOCK in _longest_free_extent(), it is
> - * possible that there is enough contiguous free space for this request.
> + * possible that there is enough contiguous free space for this request
> + * even if best length is less that the minimum length we need.
> + *
> + * If the best length won't satisfy the maximum length we requested,
> + * then use it as the minimum length so we get as large an allocation
> + * as possible.
> */
> if (blen < ap->minlen)
> - return ap->minlen;
> + blen = ap->minlen;
> + else if (blen > args->maxlen)
> + blen = args->maxlen;
>
> /*
> - * If the best seen length is less than the request length,
> - * use the best as the minimum, otherwise we've got the maxlen we
> - * were asked for.
> + * If we have alignment constraints, round the minlen down to match the
> + * constraint so that alignment will be attempted. This may reduce the
> + * allocation to smaller than was requested, so clamp the minimum to
> + * ap->minlen to allow unaligned allocation to succeed. If we are forced
> + * to align the allocation, return ENOSPC at this point because we don't
> + * have enough contiguous free space to guarantee aligned allocation.
> */
> - if (blen < args->maxlen)
> - return blen;
> - return args->maxlen;
> -
> + if (args->alignment > 1) {
> + blen = rounddown(blen, args->alignment);
> + if (blen < ap->minlen) {
> + if (args->datatype & XFS_ALLOC_FORCEALIGN)
> + return -ENOSPC;
> + blen = ap->minlen;
> + }
> + }
> + args->minlen = blen;
> + return 0;
> }
>
> static int
> @@ -3340,8 +3355,7 @@ xfs_bmap_btalloc_select_lengths(
> if (pag)
> xfs_perag_rele(pag);
>
> - args->minlen = xfs_bmap_select_minlen(ap, args, blen);
> - return error;
> + return xfs_bmap_select_minlen(ap, args, blen);
> }
>
> /* Update all inode and quota accounting for the allocation we just did. */
> @@ -3661,7 +3675,10 @@ xfs_bmap_btalloc_filestreams(
> goto out_low_space;
> }
>
> - args->minlen = xfs_bmap_select_minlen(ap, args, blen);
> + error = xfs_bmap_select_minlen(ap, args, blen);
> + if (error)
> + goto out_low_space;
> +
> if (ap->aeof && ap->offset)
> error = xfs_bmap_btalloc_at_eof(ap, args);
>
> --
> 2.31.1
>
>
