On 01/10/13 16:47, Dave Chinner wrote:
On Thu, Jan 10, 2013 at 10:41:48AM -0600, Eric Sandeen wrote:Dave Jones hit this assert when doing a compile on recent git, with CONFIG_XFS_DEBUG enabled: XFS: Assertion failed: (char *)dup - (char *)hdr == be16_to_cpu(*xfs_dir2_data_unused_tag_p(dup)), file: fs/xfs/xfs_dir2_data.c, line: 828 Upon further digging, the tag found by xfs_dir2_data_unused_tag_p(dup) contained "2" and not the proper offset, and I found that this value was changed after the memmoves under "Use a stale leaf for our new entry." in xfs_dir2_block_addname(), i.e. memmove(&blp[mid + 1],&blp[mid], (highstale - mid) * sizeof(*blp)); overwrote it. What has happened is that the previous call to xfs_dir2_block_compact() has rearranged things; it changes btp->count as well as the blp array. So after we make that call, we must recalculate the proper pointer to the leaf entries by making another call to xfs_dir2_block_leaf_p().Perhaps a bit of ascii art to explain it for other reviewers to save them having to spend a long time trying to understand the dir2 code? Pre-compact: dup + unused data pointer - size 72 bytes at offset 3560 | | blp + leaf entry [0] - good - at offset 3632 + leaf entry [1] - good + leaf entry [2] - stale + leaf entry [3] - good + leaf entry [4] - good + leaf entry [5] - stale + leaf entry [6] - good ..... + leaf entry [n] - stale + leaf entry [n+1] - good + block tail - points to offset 3632 Post compact (removes all but the highest stale leaf entry, adds the free space to the last unused data region): dup + unused data pointer - size 112 bytes at offset 3560 | | blp | points into unused region, not to start of leaf array | | + leaf entry [0] - good - at offset 3672 + leaf entry [1] - good + leaf entry [2] - good + leaf entry [3] - good ..... + leaf entry [n] - stale + leaf entry [n+1] - good + block tail - points to offset 3672 So as you can see, blp needs to be updated to point at offset 3672...
Thanks for the study aid - it did help explain the xfs_dir2_block_compact() code.
Reviewed-by: Mark Tinguely <tinguely@xxxxxxx> _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
