btrfs: rescue: allow ibadroots to skip bad extent tree when reading block group items

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 <wuzy001@gmail.com>
Link: https://www.spinics.net/lists/linux-btrfs/msg114424.html
Reviewed-by: Su Yue <l@damenly.su>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 5bd76a4..d5421ee 100644 (file)
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -2105,11 +2105,22 @@ static int fill_dummy_bgs(struct btrfs_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 the next one.
+                */
+               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(struct btrfs_fs_info *info)
        ret = check_chunk_block_group_mappings(info);
 error:
        btrfs_free_path(path);
+       /*
+        * We've hit some error while reading the extent tree, and have
+        * rescue=ibadroots mount option.
+        * Try to fill the tree 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;
 }