[PATCH 1/2] btrfs: convert block group refcount to refcount_t

[Josef Bacik <josef@toxicpanda.com>]

I was experimenting with some new allocator changes and I noticed that I
was getting a UAF with the block groups.  In order to help figure this
out I converted the block group to use the refcount_t infrastructure.
This is a generally good idea anyway, so kill the atomic and use
refcount_t so we can get the benefit of loud complaints when refcounting
goes wrong.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/block-group.c | 8 ++++----
 fs/btrfs/block-group.h | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 09b796a081dd..7c0075413b08 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -118,12 +118,12 @@ u64 btrfs_get_alloc_profile(struct btrfs_fs_info *fs_info, u64 orig_flags)
 
 void btrfs_get_block_group(struct btrfs_block_group *cache)
 {
-	atomic_inc(&cache->count);
+	refcount_inc(&cache->count);
 }
 
 void btrfs_put_block_group(struct btrfs_block_group *cache)
 {
-	if (atomic_dec_and_test(&cache->count)) {
+	if (refcount_dec_and_test(&cache->count)) {
 		WARN_ON(cache->pinned > 0);
 		WARN_ON(cache->reserved > 0);
 
@@ -1805,7 +1805,7 @@ static struct btrfs_block_group *btrfs_create_block_group_cache(
 
 	cache->discard_index = BTRFS_DISCARD_INDEX_UNUSED;
 
-	atomic_set(&cache->count, 1);
+	refcount_set(&cache->count, 1);
 	spin_lock_init(&cache->lock);
 	init_rwsem(&cache->data_rwsem);
 	INIT_LIST_HEAD(&cache->list);
@@ -3427,7 +3427,7 @@ int btrfs_free_block_groups(struct btrfs_fs_info *info)
 		ASSERT(list_empty(&block_group->dirty_list));
 		ASSERT(list_empty(&block_group->io_list));
 		ASSERT(list_empty(&block_group->bg_list));
-		ASSERT(atomic_read(&block_group->count) == 1);
+		ASSERT(refcount_read(&block_group->count) == 1);
 		btrfs_put_block_group(block_group);
 
 		spin_lock(&info->block_group_cache_lock);
diff --git a/fs/btrfs/block-group.h b/fs/btrfs/block-group.h
index b6ee70a039c7..705e48050163 100644
--- a/fs/btrfs/block-group.h
+++ b/fs/btrfs/block-group.h
@@ -115,7 +115,7 @@ struct btrfs_block_group {
 	struct list_head list;
 
 	/* Usage count */
-	atomic_t count;
+	refcount_t count;
 
 	/*
 	 * List of struct btrfs_free_clusters for this block group.
-- 
2.24.1