[PATCH] blk-mq: fix double-free in error path

[Tony Battersby]

If the allocation of bt->bs fails, then bt->map can be freed twice, once
in blk_mq_init_bitmap_tags() -> bt_alloc(), and once in
blk_mq_init_bitmap_tags() -> bt_free().  Fix by setting the pointer to
NULL after the first free.

Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Tony Battersby <tonyb@xxxxxxxxxxxxxxx>
---

For inclusion in kernel 3.20.

--- linux-3.19.0/block/blk-mq-tag.c.orig	2015-02-08 21:54:22.000000000 -0500
+++ linux-3.19.0/block/blk-mq-tag.c	2015-02-10 09:42:38.000000000 -0500
@@ -509,6 +509,7 @@ static int bt_alloc(struct blk_mq_bitmap
 	bt->bs = kzalloc(BT_WAIT_QUEUES * sizeof(*bt->bs), GFP_KERNEL);
 	if (!bt->bs) {
 		kfree(bt->map);
+		bt->map = NULL;
 		return -ENOMEM;
 	}
 

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