[PATCH] btrfs: drop recovered reloc root refs on recovery failure

[Guanghui Yang]

During relocation recovery, each fs root gets a reference to its relocation
root. If loading or adding a later root fails, or if the first transaction
commit fails, btrfs_recover_relocation() jumps to out_unset before
merge_reloc_roots() and clean_dirty_subvols().

put_reloc_control() drops the list-owned relocation root references, but it
does not clear fs_root->reloc_root or drop the references owned by those
pointers. Mount cleanup only drops them when BTRFS_FS_ERROR is set, so an
error such as -ENOMEM while processing a later root can leave references
behind.

Keep temporary references to the fs roots associated during recovery. On
failure, clear their reloc_root pointers and drop the corresponding
references. Once the first transaction commit succeeds, drop only the
temporary fs root references and let the normal merge and cleanup paths
handle the relocation roots.

Fault injection on a pending-relocation image confirmed the cleanup gap.
With an injected first-commit failure, 25 fs roots had reloc_root set with
fs_error=0. With this fix, the same failure path drops that count to 0
before mount fails.

Fixes: f44deb7442ed ("btrfs: hold a ref on the root->reloc_root")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Guanghui Yang <3497809730@xxxxxx>
---
 fs/btrfs/relocation.c | 32 ++++++++++++++++++++++++++++----
 1 file changed, 28 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index fb85bc8b345c..0d71cd80917f 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -5525,6 +5525,25 @@ static noinline_for_stack int mark_garbage_root(struct btrfs_root *root)
 	return ret;
 }
 
+static void release_recovered_fs_roots(struct list_head *roots,
+				       bool drop_reloc_refs)
+{
+	struct btrfs_root *root;
+	struct btrfs_root *next;
+
+	list_for_each_entry_safe(root, next, roots, reloc_dirty_list) {
+		list_del_init(&root->reloc_dirty_list);
+		if (drop_reloc_refs) {
+			struct btrfs_root *reloc_root = root->reloc_root;
+
+			ASSERT(reloc_root);
+			root->reloc_root = NULL;
+			btrfs_put_root(reloc_root);
+		}
+		btrfs_put_root(root);
+	}
+}
+
 /*
  * recover relocation interrupted by system crash.
  *
@@ -5534,6 +5553,7 @@ static noinline_for_stack int mark_garbage_root(struct btrfs_root *root)
 int btrfs_recover_relocation(struct btrfs_fs_info *fs_info)
 {
 	LIST_HEAD(reloc_roots);
+	LIST_HEAD(recovered_roots);
 	struct btrfs_key key;
 	struct btrfs_root *fs_root;
 	struct btrfs_root *reloc_root;
@@ -5650,7 +5670,7 @@ int btrfs_recover_relocation(struct btrfs_fs_info *fs_info)
 			ret = PTR_ERR(fs_root);
 			list_add_tail(&reloc_root->root_list, &reloc_roots);
 			btrfs_end_transaction(trans);
-			goto out_unset;
+			goto out_drop_reloc_refs;
 		}
 
 		ret = __add_reloc_root(reloc_root, rc);
@@ -5659,15 +5679,17 @@ int btrfs_recover_relocation(struct btrfs_fs_info *fs_info)
 			list_add_tail(&reloc_root->root_list, &reloc_roots);
 			btrfs_put_root(fs_root);
 			btrfs_end_transaction(trans);
-			goto out_unset;
+			goto out_drop_reloc_refs;
 		}
+		ASSERT(list_empty(&fs_root->reloc_dirty_list));
 		fs_root->reloc_root = btrfs_grab_root(reloc_root);
-		btrfs_put_root(fs_root);
+		list_add_tail(&fs_root->reloc_dirty_list, &recovered_roots);
 	}
 
 	ret = btrfs_commit_transaction(trans);
 	if (ret)
-		goto out_unset;
+		goto out_drop_reloc_refs;
+	release_recovered_fs_roots(&recovered_roots, false);
 
 	merge_reloc_roots(rc);
 
@@ -5683,6 +5705,8 @@ int btrfs_recover_relocation(struct btrfs_fs_info *fs_info)
 	ret2 = clean_dirty_subvols(rc);
 	if (ret2 < 0 && !ret)
 		ret = ret2;
+out_drop_reloc_refs:
+	release_recovered_fs_roots(&recovered_roots, true);
 out_unset:
 	unset_reloc_control(rc);
 	reloc_chunk_end(fs_info);
-- 
2.34.1