Re: [PATCH v4] btrfs: rescue: allow ibadroots to skip bad extent tree when reading block group items
From: Su Yue <hidden>
Date: 2021-07-19 05:53:10
On Mon 19 Jul 2021 at 13:43, Qu Wenruo [off-list ref] wrote:
When extent tree gets corrupted, normally it's not extent tree root, but one toasted tree leaf/node. In that case, rescue=ibadroots mount option won't help as it can only handle the extent tree root corruption. This patch will enhance the behavior by: - Allow fill_dummy_bgs() to ignore -EEXIST error This means we may have some block group items read from disk, but then hit some error halfway. - Fallback to fill_dummy_bgs() if any error gets hit in btrfs_read_block_groups() Of course, this still needs rescue=ibadroots mount option. With that, rescue=ibadroots can handle extent tree corruption more gracefully and allow a better recover chance. Reported-by: Zhenyu Wu <redacted> Link: https://www.spinics.net/lists/linux-btrfs/msg114424.html Signed-off-by: Qu Wenruo <redacted>
LGTM. Reviewed-by: Su Yue <redacted> -- Su
quoted hunk ↗ jump to hunk
--- Changelog: v2: - Don't try to fill with dummy block groups when we hit ENOMEM v3: - Remove a dead condition The empty fs_info->extent_root case has already been handled. v4: - Skip to next block group if we hit EEXIST when inserting the block group cache --- fs/btrfs/block-group.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c index 5bd76a45037e..758ba856f8c6 100644 --- a/fs/btrfs/block-group.c +++ b/fs/btrfs/block-group.c@@ -2105,11 +2105,22 @@ static int fill_dummy_bgs(structbtrfs_fs_info *fs_info) bg->used = em->len; bg->flags = map->type; ret = btrfs_add_block_group_cache(fs_info, bg); + /* + * We may have some valid block group cache added already, in + * that case we skip to next bg. + */ + if (ret == -EEXIST) { + ret = 0; + btrfs_put_block_group(bg); + continue; + } + if (ret) { btrfs_remove_free_space_cache(bg); btrfs_put_block_group(bg); break; } + btrfs_update_space_info(fs_info, bg->flags, em->len, em->len, 0, 0, &space_info); bg->space_info = space_info;@@ -2212,6 +2223,14 @@ int btrfs_read_block_groups(structbtrfs_fs_info *info) ret = check_chunk_block_group_mappings(info); error: btrfs_free_path(path); + /* + * We hit some error reading the extent tree, and have rescue=ibadroots + * mount option. + * Try to fill using dummy block groups so that the user can continue + * to mount and grab their data. + */ + if (ret && btrfs_test_opt(info, IGNOREBADROOTS)) + ret = fill_dummy_bgs(info); return ret; }