diff --git a/fs/btrfs/block-rsv.c b/fs/btrfs/block-rsv.c
index 77684c5e0c8b..db8da4e7b228 100644
--- a/fs/btrfs/block-rsv.c
+++ b/fs/btrfs/block-rsv.c
@@ -486,7 +486,7 @@ struct btrfs_block_rsv *btrfs_use_block_rsv(struct btrfs_trans_handle *trans,
 
 	block_rsv = get_block_rsv(trans, root);
 
-	if (unlikely(block_rsv->size == 0))
+	if (unlikely(btrfs_block_rsv_size(block_rsv) == 0))
 		goto try_reserve;
 again:
 	ret = btrfs_block_rsv_use_bytes(block_rsv, blocksize);
diff --git a/fs/btrfs/block-rsv.h b/fs/btrfs/block-rsv.h
index fb440a074700..43a9a6b5a79f 100644
--- a/fs/btrfs/block-rsv.h
+++ b/fs/btrfs/block-rsv.h
@@ -117,4 +117,20 @@ static inline u64 btrfs_block_rsv_reserved(struct btrfs_block_rsv *rsv)
 	return ret;
 }
 
+/*
+ * Get the size of a block reserve in a context where getting a stale value is
+ * acceptable, instead of accessing it directly and trigger data race warning
+ * from KCSAN.
+ */
+static inline u64 btrfs_block_rsv_size(struct btrfs_block_rsv *rsv)
+{
+	u64 ret;
+
+	spin_lock(&rsv->lock);
+	ret = rsv->size;
+	spin_unlock(&rsv->lock);
+
+	return ret;
+}
+
 #endif /* BTRFS_BLOCK_RSV_H */