[PATCH] bcache: Fix __bch_btree_node_alloc to make the failure behavior consistent

[Zheng Wang]

In some specific situation, the return value of __bch_btree_node_alloc may
be NULL. This may lead to poential NULL pointer dereference in caller
 function like a calling chaion :
 btree_split->bch_btree_node_alloc->__bch_btree_node_alloc.

Fix it by initialize return value in __bch_btree_node_alloc before return.

Fixes: cafe56359144 ("bcache: A block layer cache")
Signed-off-by: Zheng Wang <zyytlz.wz@xxxxxxx>
---
 drivers/md/bcache/btree.c | 10 ++++++----
 drivers/md/bcache/super.c |  2 +-
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 147c493a989a..35346c1d7c3c 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -1090,10 +1090,12 @@ struct btree *__bch_btree_node_alloc(struct cache_set *c, struct btree_op *op,
 				     struct btree *parent)
 {
 	BKEY_PADDED(key) k;
-	struct btree *b = ERR_PTR(-EAGAIN);
+	struct btree *b;
 
 	mutex_lock(&c->bucket_lock);
 retry:
+	/* return ERR_PTR(-EAGAIN) when it fails */
+	b = ERR_PTR(-EAGAIN);
 	if (__bch_bucket_alloc_set(c, RESERVE_BTREE, &k.key, wait))
 		goto err;
 
@@ -1138,7 +1140,7 @@ static struct btree *btree_node_alloc_replacement(struct btree *b,
 {
 	struct btree *n = bch_btree_node_alloc(b->c, op, b->level, b->parent);
 
-	if (!IS_ERR_OR_NULL(n)) {
+	if (!IS_ERR(n)) {
 		mutex_lock(&n->write_lock);
 		bch_btree_sort_into(&b->keys, &n->keys, &b->c->sort);
 		bkey_copy_key(&n->key, &b->key);
@@ -1352,7 +1354,7 @@ static int btree_gc_coalesce(struct btree *b, struct btree_op *op,
 
 	for (i = 0; i < nodes; i++) {
 		new_nodes[i] = btree_node_alloc_replacement(r[i].b, NULL);
-		if (IS_ERR_OR_NULL(new_nodes[i]))
+		if (IS_ERR(new_nodes[i]))
 			goto out_nocoalesce;
 	}
 
@@ -1669,7 +1671,7 @@ static int bch_btree_gc_root(struct btree *b, struct btree_op *op,
 	if (should_rewrite) {
 		n = btree_node_alloc_replacement(b, NULL);
 
-		if (!IS_ERR_OR_NULL(n)) {
+		if (!IS_ERR(n)) {
 			bch_btree_node_write_sync(n);
 
 			bch_btree_set_root(n);
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index ba3909bb6bea..92de714fe75e 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -2088,7 +2088,7 @@ static int run_cache_set(struct cache_set *c)
 
 		err = "cannot allocate new btree root";
 		c->root = __bch_btree_node_alloc(c, NULL, 0, true, NULL);
-		if (IS_ERR_OR_NULL(c->root))
+		if (IS_ERR(c->root))
 			goto err;
 
 		mutex_lock(&c->root->write_lock);
-- 
2.25.1