On 6.11.18 г. 16:40 ч., Nikolay Borisov wrote:
> When a metadata read is served the endio routine btree_readpage_end_io_hook
> is called which eventually runs the tree-checker. If tree-checker fails
> to validate the read eb then it sets EXTENT_BUFFER_CORRUPT flag. This
> leads to btree_read_extent_buffer_pages wrongly assuming that all
> available copies of this extent buffer are wrong and failing prematurely.
> Fix this modify btree_read_extent_buffer_pages to read all copies of
> the data.
>
> This failure was exhibitted in xfstests btrfs/124 which would
> spuriously fail its balance operations. The reason was that when balance
> was run following re-introduction of the missing raid1 disk
> __btrfs_map_block would map the read request to stripe 0, which
> corresponded to devid 2 (the disk which is being removed in the test):
>
> item 2 key (FIRST_CHUNK_TREE CHUNK_ITEM 3553624064) itemoff 15975 itemsize 112
> length 1073741824 owner 2 stripe_len 65536 type DATA|RAID1
> io_align 65536 io_width 65536 sector_size 4096
> num_stripes 2 sub_stripes 1
> stripe 0 devid 2 offset 2156920832
> dev_uuid 8466c350-ed0c-4c3b-b17d-6379b445d5c8
> stripe 1 devid 1 offset 3553624064
> dev_uuid 1265d8db-5596-477e-af03-df08eb38d2ca
>
> This caused read requests for a checksum item that to be routed to the
> stale disk which triggered the aforementioned logic involving
> EXTENT_BUFFER_CORRUPT flag. This then triggered cascading failures of
> the balance operation.
>
> Signed-off-by: Nikolay Borisov <nborisov@xxxxxxxx>
> Suggested-by: Qu Wenruo <wqu@xxxxxxxx>
> Fixes: a826d6dcb32d ("Btrfs: check items for correctness as we search")
> ---
> fs/btrfs/disk-io.c | 11 +----------
> 1 file changed, 1 insertion(+), 10 deletions(-)
>
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index 00ee5e37e989..279c6dbcc736 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -477,9 +477,9 @@ static int btree_read_extent_buffer_pages(struct btrfs_fs_info *fs_info,
> int mirror_num = 0;
> int failed_mirror = 0;
>
> - clear_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags);
> io_tree = &BTRFS_I(fs_info->btree_inode)->io_tree;
> while (1) {
> + clear_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags);
> ret = read_extent_buffer_pages(io_tree, eb, WAIT_COMPLETE,
> mirror_num);
> if (!ret) {
Qu,
Do you think it makes sense to do refactoring like below in
a follow up patch:
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 279c6dbcc736..9891e13a2b6f 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -482,16 +482,11 @@ static int btree_read_extent_buffer_pages(struct btrfs_fs_info *fs_info,
clear_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags);
ret = read_extent_buffer_pages(io_tree, eb, WAIT_COMPLETE,
mirror_num);
- if (!ret) {
- if (verify_parent_transid(io_tree, eb,
- parent_transid, 0))
- ret = -EIO;
- else if (verify_level_key(fs_info, eb, level,
- first_key, parent_transid))
- ret = -EUCLEAN;
- else
+ if (!ret &&
+ !verify_parent_transid(io_tree, eb, parent_transid, 0) &&
+ !verify_level_key(fs_info, eb, level, first_key,
+ parent_transid))
break;
- }
since the ret value doesn't really have any meaning or perhaps the
verify_level_key and ret = -EUCLEAN could be reteinaed as well as the
if (ret == EUCLEAN) break logic ?
> @@ -493,15 +493,6 @@ static int btree_read_extent_buffer_pages(struct btrfs_fs_info *fs_info,
> break;
> }
>
> - /*
> - * This buffer's crc is fine, but its contents are corrupted, so
> - * there is no reason to read the other copies, they won't be
> - * any less wrong.
> - */
> - if (test_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags) ||
> - ret == -EUCLEAN)
> - break;
> -
> num_copies = btrfs_num_copies(fs_info,
> eb->start, eb->len);
> if (num_copies == 1)
>
