dm cache policy mq: a few small fixes

Rename takeout_queue to concat_queue.

Fix a harmless bug in mq policies pop() function.  Currently pop()
always succeeds, with up coming changes this wont be the case.

Fix typo in comment above pre_cache_to_cache prototype.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-cache-policy-mq.c

@@ -311,7 +311,7 @@ struct mq_policy {
 
 /*----------------------------------------------------------------*/
 /* Free/alloc mq cache entry structures. */
-static void takeout_queue(struct list_head *lh, struct queue *q)
+static void concat_queue(struct list_head *lh, struct queue *q)
 {
 	unsigned level;
 
@@ -323,8 +323,8 @@ static void free_entries(struct mq_policy *mq)
 {
 	struct entry *e, *tmp;
 
-	takeout_queue(&mq->free, &mq->pre_cache);
-	takeout_queue(&mq->free, &mq->cache);
+	concat_queue(&mq->free, &mq->pre_cache);
+	concat_queue(&mq->free, &mq->cache);
 
 	list_for_each_entry_safe(e, tmp, &mq->free, list)
 		kmem_cache_free(mq_entry_cache, e);
@@ -531,14 +531,16 @@ static void del(struct mq_policy *mq, struct entry *e)
  */
 static struct entry *pop(struct mq_policy *mq, struct queue *q)
 {
-	struct entry *e = container_of(queue_pop(q), struct entry, list);
+	struct entry *e;
+	struct list_head *h = queue_pop(q);
 
-	if (e) {
-		hash_remove(e);
+	if (!h)
+		return NULL;
 
+	e = container_of(h, struct entry, list);
+	hash_remove(e);
 	if (e->in_cache)
 		free_cblock(mq, e->cblock);
-	}
 
 	return e;
 }
@@ -697,7 +699,7 @@ static int cache_entry_found(struct mq_policy *mq,
 }
 
 /*
- * Moves and entry from the pre_cache to the cache.  The main work is
+ * Moves an entry from the pre_cache to the cache.  The main work is
  * finding which cache block to use.
  */
 static int pre_cache_to_cache(struct mq_policy *mq, struct entry *e,