diff mbox series

[v2,4/5] btrfs: explicitly ref count block_group on new_bgs list

Message ID 5ea6c280fbe91b772802313847967ee4c2e89201.1741636986.git.boris@bur.io (mailing list archive)
State New
Headers show
Series btrfs: block_group refcounting fixes | expand

Commit Message

Boris Burkov March 10, 2025, 8:07 p.m. UTC 
All other users of the bg_list list_head inc the refcount when adding to
a list and dec it when deleting from the list. Just for the sake of
uniformity and to try to avoid refcounting bugs, do it for this list as
well.

This does not fix any known ref-counting bug, as the reference belongs
to a single task (trans_handle is not shared and this represents
trans_handle->new_bgs linkage) and will not lose its original refcount
while that thread is running. And BLOCK_GROUP_FLAG_NEW protects against
ref-counting errors "moving" the block group to the unused list without
taking a ref.

With that said, I still believe it is simpler to just hold the extra ref
count for this list user as well.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Boris Burkov <boris@bur.io>
---
 fs/btrfs/block-group.c | 2 ++
 fs/btrfs/transaction.c | 1 +
 2 files changed, 3 insertions(+)
diff mbox series

Patch

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 2db1497b58d9..e4071897c9a8 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -2801,6 +2801,7 @@  void btrfs_create_pending_block_groups(struct btrfs_trans_handle *trans)
 		spin_lock(&fs_info->unused_bgs_lock);
 		list_del_init(&block_group->bg_list);
 		clear_bit(BLOCK_GROUP_FLAG_NEW, &block_group->runtime_flags);
+		btrfs_put_block_group(block_group);
 		spin_unlock(&fs_info->unused_bgs_lock);
 
 		/*
@@ -2939,6 +2940,7 @@  struct btrfs_block_group *btrfs_make_block_group(struct btrfs_trans_handle *tran
 	}
 #endif
 
+	btrfs_get_block_group(cache);
 	list_add_tail(&cache->bg_list, &trans->new_bgs);
 	btrfs_inc_delayed_refs_rsv_bg_inserts(fs_info);
 
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 470dfc3a1a5c..f26a394a9ec5 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -2108,6 +2108,7 @@  static void btrfs_cleanup_pending_block_groups(struct btrfs_trans_handle *trans)
 		*/
 	       spin_lock(&fs_info->unused_bgs_lock);
                list_del_init(&block_group->bg_list);
+	       btrfs_put_block_group(block_group);
 	       spin_unlock(&fs_info->unused_bgs_lock);
        }
 }