On 1/11/13 4:11 PM, Mark Tinguely wrote: > 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. Feel free to add that to the commit . . . Thanks, -Eric > Reviewed-by: Mark Tinguely <tinguely@xxxxxxx> > > _______________________________________________ > xfs mailing list > xfs@xxxxxxxxxxx > http://oss.sgi.com/mailman/listinfo/xfs > _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
