diff options
| -rw-r--r-- | fs/btrfs/tree-log.c | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c index 6d650468d21a..1bbaace73383 100644 --- a/fs/btrfs/tree-log.c +++ b/fs/btrfs/tree-log.c @@ -722,12 +722,66 @@ static noinline int replay_one_extent(struct btrfs_trans_handle *trans, &ordered_sums, 0); if (ret) goto out; + /* + * Now delete all existing cums in the csum root that + * cover our range. We do this because we can have an + * extent that is completely referenced by one file + * extent item and partially referenced by another + * file extent item (like after using the clone or + * extent_same ioctls). In this case if we end up doing + * the replay of the one that partially references the + * extent first, and we do not do the csum deletion + * below, we can get 2 csum items in the csum tree that + * overlap each other. For example, imagine our log has + * the two following file extent items: + * + * key (257 EXTENT_DATA 409600) + * extent data disk byte 12845056 nr 102400 + * extent data offset 20480 nr 20480 ram 102400 + * + * key (257 EXTENT_DATA 819200) + * extent data disk byte 12845056 nr 102400 + * extent data offset 0 nr 102400 ram 102400 + * + * Where the second one fully references the 100K extent + * that starts at disk byte 12845056, and the log tree + * has a single csum item that covers the entire range + * of the extent: + * + * key (EXTENT_CSUM EXTENT_CSUM 12845056) itemsize 100 + * + * After the first file extent item is replayed, the + * csum tree gets the following csum item: + * + * key (EXTENT_CSUM EXTENT_CSUM 12865536) itemsize 20 + * + * Which covers the 20K sub-range starting at offset 20K + * of our extent. Now when we replay the second file + * extent item, if we do not delete existing csum items + * that cover any of its blocks, we end up getting two + * csum items in our csum tree that overlap each other: + * + * key (EXTENT_CSUM EXTENT_CSUM 12845056) itemsize 100 + * key (EXTENT_CSUM EXTENT_CSUM 12865536) itemsize 20 + * + * Which is a problem, because after this anyone trying + * to lookup up for the checksum of any block of our + * extent starting at an offset of 40K or higher, will + * end up looking at the second csum item only, which + * does not contain the checksum for any block starting + * at offset 40K or higher of our extent. + */ while (!list_empty(&ordered_sums)) { struct btrfs_ordered_sum *sums; sums = list_entry(ordered_sums.next, struct btrfs_ordered_sum, list); if (!ret) + ret = btrfs_del_csums(trans, + root->fs_info->csum_root, + sums->bytenr, + sums->len); + if (!ret) ret = btrfs_csum_file_blocks(trans, root->fs_info->csum_root, sums); |