On Tue, Feb 23, 2021 at 03:46:35PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> Otherwise it doesn't correctly calculate the number of vectors
> in a logged buffer that has a contiguous map that gets split into
> multiple regions because the range spans discontigous memory.
>
> Probably never been hit in practice - we don't log contiguous ranges
> on unmapped buffers (inode clusters).
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
Subtle.
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
--D
> ---
> fs/xfs/xfs_buf_item.c | 38 +++++++++++++++++++-------------------
> 1 file changed, 19 insertions(+), 19 deletions(-)
>
> diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c
> index 0628a65d9c55..91dc7d8c9739 100644
> --- a/fs/xfs/xfs_buf_item.c
> +++ b/fs/xfs/xfs_buf_item.c
> @@ -55,6 +55,18 @@ xfs_buf_log_format_size(
> (blfp->blf_map_size * sizeof(blfp->blf_data_map[0]));
> }
>
> +static inline bool
> +xfs_buf_item_straddle(
> + struct xfs_buf *bp,
> + uint offset,
> + int next_bit,
> + int last_bit)
> +{
> + return xfs_buf_offset(bp, offset + (next_bit << XFS_BLF_SHIFT)) !=
> + (xfs_buf_offset(bp, offset + (last_bit << XFS_BLF_SHIFT)) +
> + XFS_BLF_CHUNK);
> +}
> +
> /*
> * Return the number of log iovecs and space needed to log the given buf log
> * item segment.
> @@ -67,6 +79,7 @@ STATIC void
> xfs_buf_item_size_segment(
> struct xfs_buf_log_item *bip,
> struct xfs_buf_log_format *blfp,
> + uint offset,
> int *nvecs,
> int *nbytes)
> {
> @@ -101,12 +114,8 @@ xfs_buf_item_size_segment(
> */
> if (next_bit == -1) {
> break;
> - } else if (next_bit != last_bit + 1) {
> - last_bit = next_bit;
> - (*nvecs)++;
> - } else if (xfs_buf_offset(bp, next_bit * XFS_BLF_CHUNK) !=
> - (xfs_buf_offset(bp, last_bit * XFS_BLF_CHUNK) +
> - XFS_BLF_CHUNK)) {
> + } else if (next_bit != last_bit + 1 ||
> + xfs_buf_item_straddle(bp, offset, next_bit, last_bit)) {
> last_bit = next_bit;
> (*nvecs)++;
> } else {
> @@ -141,8 +150,10 @@ xfs_buf_item_size(
> int *nbytes)
> {
> struct xfs_buf_log_item *bip = BUF_ITEM(lip);
> + struct xfs_buf *bp = bip->bli_buf;
> int i;
> int bytes;
> + uint offset = 0;
>
> ASSERT(atomic_read(&bip->bli_refcount) > 0);
> if (bip->bli_flags & XFS_BLI_STALE) {
> @@ -184,8 +195,9 @@ xfs_buf_item_size(
> */
> bytes = 0;
> for (i = 0; i < bip->bli_format_count; i++) {
> - xfs_buf_item_size_segment(bip, &bip->bli_formats[i],
> + xfs_buf_item_size_segment(bip, &bip->bli_formats[i], offset,
> nvecs, &bytes);
> + offset += BBTOB(bp->b_maps[i].bm_len);
> }
>
> /*
> @@ -212,18 +224,6 @@ xfs_buf_item_copy_iovec(
> nbits * XFS_BLF_CHUNK);
> }
>
> -static inline bool
> -xfs_buf_item_straddle(
> - struct xfs_buf *bp,
> - uint offset,
> - int next_bit,
> - int last_bit)
> -{
> - return xfs_buf_offset(bp, offset + (next_bit << XFS_BLF_SHIFT)) !=
> - (xfs_buf_offset(bp, offset + (last_bit << XFS_BLF_SHIFT)) +
> - XFS_BLF_CHUNK);
> -}
> -
> static void
> xfs_buf_item_format_segment(
> struct xfs_buf_log_item *bip,
> --
> 2.28.0
>
