xfs: fix segment in xfs_buf_item_format_segment

Not every segment in a multi-segment buffer is dirty in a
transaction and they will not be outputted. The assert in
xfs_buf_item_format_segment() that checks for the at least
one chunk of data in the segment to be used is not necessary
true for multi-segmented buffers.

Signed-off-by: Mark Tinguely <tinguely@sgi.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

1 files changed, 15 insertions, 5 deletions

diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c
index 1975b3d9007a..c48e60bd857d 100644
--- a/fs/xfs/xfs_buf_item.c
+++ b/fs/xfs/xfs_buf_item.c
@@ -287,6 +287,17 @@ xfs_buf_item_format_segment(
          */
         base_size = offsetof(struct xfs_buf_log_format, blf_data_map) +
                         (blfp->blf_map_size * sizeof(blfp->blf_data_map[0]));
+
+        nvecs = 0;
+        first_bit = xfs_next_bit(blfp->blf_data_map, blfp->blf_map_size, 0);
+        if (!(bip->bli_flags & XFS_BLI_STALE) && first_bit == -1) {
+                /*
+                 * If the map is not be dirty in the transaction, mark
+                 * the size as zero and do not advance the vector pointer.
+                 */
+                goto out;
+        }
+
         vecp->i_addr = blfp;
         vecp->i_len = base_size;
         vecp->i_type = XLOG_REG_TYPE_BFORMAT;
@@ -301,15 +312,13 @@ xfs_buf_item_format_segment(
                  */
                 trace_xfs_buf_item_format_stale(bip);
                 ASSERT(blfp->blf_flags & XFS_BLF_CANCEL);
-                blfp->blf_size = nvecs;
-                return vecp;
+                goto out;
         }
 
         /*
          * Fill in an iovec for each set of contiguous chunks.
          */
-        first_bit = xfs_next_bit(blfp->blf_data_map, blfp->blf_map_size, 0);
-        ASSERT(first_bit != -1);
+
         last_bit = first_bit;
         nbits = 1;
         for (;;) {
@@ -371,7 +380,8 @@ xfs_buf_item_format_segment(
                         nbits++;
                 }
         }
-        bip->__bli_format.blf_size = nvecs;
+out:
+        blfp->blf_size = nvecs;
         return vecp;
 }