check_fs_roots() will check all fs trees again if fs_info->tree_root
have been cowed.
It is inefficient if there are many subvolumes in filesystem.

And it also causes dead loop while repairing
fuzz-tests/images/bko-161811.raw:
=============================
ERROR: DIR_ITEM[256 1167283096] name  namelen 32 filetype 1 mismatch with its 
hash, wanted 1167283096 have 709597396
invalid location in dir item 0
root 5 root dir 256 error
root 5 inode 256 errors 10, odd dir item
Failed to reset nlink for inode 18446744073709551361: No such file or directory
        unresolved ref dir 256 index 0 namelen 32 name  filetype 1 errors 106, 
no dir index, no inode ref, name too long
ERROR: DIR_ITEM[256 1167283096] name  namelen 32 filetype 1 mismatch with its 
hash, wanted 1167283096 have 709597396
invalid location in dir item 0
root 5 root dir 256 error
root 5 inode 256 errors 10, odd dir item
Failed to reset nlink for inode 18446744073709551361: No such file or directory
        unresolved ref dir 256 index 0 namelen 32 name  filetype 1 errors 106, 
no dir index, no inode ref, name too long
ERROR: DIR_ITEM[256 1167283096] name  namelen 32 filetype 1 mismatch with its 
hash, wanted 1167283
...
==============================

Process of the dead loop:
1) check_fs_root() failed to repair the inode.
2) btrfs_commit_transaction() did cow of the fs_info->tree_root
3) check_fs_roots() restarted to check fs tree.
4) goto 1).

Introduce a variable @prev_key to record last checked root_item.
If check_fs_root() failed, go to check the next fs_tree instead of
trying it again and again.

Signed-off-by: Su Yue <suy.f...@cn.fujitsu.com>
---
 cmds-check.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/cmds-check.c b/cmds-check.c
index 68348ae94c8b..d149608acde2 100644
--- a/cmds-check.c
+++ b/cmds-check.c
@@ -4587,6 +4587,7 @@ static int check_fs_roots(struct btrfs_fs_info *fs_info,
 {
        struct btrfs_path path;
        struct btrfs_key key;
+       struct btrfs_key prev_key;
        struct walk_control wc;
        struct extent_buffer *leaf, *tree_node;
        struct btrfs_root *tmp_root;
@@ -4609,19 +4610,21 @@ static int check_fs_roots(struct btrfs_fs_info *fs_info,
        cache_tree_init(&wc.shared);
        btrfs_init_path(&path);
 
+       prev_key.offset = 0;
+       prev_key.objectid = 0;
+       prev_key.type = BTRFS_ROOT_ITEM_KEY;
 again:
-       key.offset = 0;
-       key.objectid = 0;
-       key.type = BTRFS_ROOT_ITEM_KEY;
+       key = prev_key;
        ret = btrfs_search_slot(NULL, tree_root, &key, &path, 0, 0);
        if (ret < 0) {
                err = 1;
                goto out;
        }
+       if (!ret)
+               path.slots[0]++;
        tree_node = tree_root->node;
        while (1) {
                if (tree_node != tree_root->node) {
-                       free_root_recs_tree(root_cache);
                        btrfs_release_path(&path);
                        goto again;
                }
@@ -4636,6 +4639,9 @@ again:
                        leaf = path.nodes[0];
                }
                btrfs_item_key_to_cpu(leaf, &key, path.slots[0]);
+               /* save key */
+               prev_key = key;
+
                if (key.type == BTRFS_ROOT_ITEM_KEY &&
                    fs_root_objectid(key.objectid)) {
                        if (key.objectid == BTRFS_TREE_RELOC_OBJECTID) {
@@ -4654,6 +4660,8 @@ again:
                        if (ret == -EAGAIN) {
                                free_root_recs_tree(root_cache);
                                btrfs_release_path(&path);
+                               prev_key.objectid = 0;
+                               prev_key.offset = 0;
                                goto again;
                        }
                        if (ret)
-- 
2.15.0



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