btrfs: explicitly ref count block_group on new_bgs list

All other users of the bg_list list_head increment the refcount when
adding to a list and decrement 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>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index f3a22b660fd38318b5613f0386ed683231b3b409..221df35da49bef11baa2a6ad13707aece778b485 100644 (file)
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -2801,6 +2801,7 @@ next:
                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 470dfc3a1a5cbebc51db27474cf4dcb3a9945b98..f26a394a9ec5f0d568551c707974a7d8f413eb3b 100644 (file)
--- 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);
        }
 }