[RESEND PATCH v3] 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")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Zheng Wang <zyytlz.wz@xxxxxxx>
---
v3:
- Add Cc: stable@xxxxxxxxxxxxxxx suggested by Eric
v2:
- split patch v1 into two patches to make it clearer suggested by Coly Li
---
 drivers/md/bcache/btree.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 147c493a989a..cae25e74b9e0 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;
 
-- 
2.25.1