[PATCH 2/2] block: return error if too many reserved tags are requested

[Robert Elliott <relliott@beardog.cce.hp.com>]

From: Robert Elliott <elliott@hp.com>

Make blk_mq_alloc_tag_set return an error if set->reserved_tags
is greater than BLK_MQ_MAX_DEPTH minus the minimum number of
tags, since:
* set->queue_depth is truncated to that value
* set->reserved_tags needs to be less than set->queue_depth

Signed-off-by: Robert Elliott <elliott@hp.com>
---
 block/blk-mq.c |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index c49fe00..dc2970d 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1936,16 +1936,18 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
 		return -EINVAL;
 	if (!set->queue_depth)
 		return -EINVAL;
+	if (set->reserved_tags > BLK_MQ_MAX_DEPTH - BLK_MQ_TAG_MIN)
+		return -EINVAL;
 	if (set->queue_depth < set->reserved_tags + BLK_MQ_TAG_MIN)
 		return -EINVAL;
 
 	if (!set->nr_hw_queues || !set->ops->queue_rq || !set->ops->map_queue)
 		return -EINVAL;
 
-	if (set->queue_depth > BLK_MQ_MAX_DEPTH) {
+	if (set->queue_depth > BLK_MQ_MAX_DEPTH - set->reserved_tags) {
+		set->queue_depth = BLK_MQ_MAX_DEPTH - set->reserved_tags;
 		pr_info("blk-mq: reduced tag depth to %u\n",
-			BLK_MQ_MAX_DEPTH);
-		set->queue_depth = BLK_MQ_MAX_DEPTH;
+			set->queue_depth);
 	}
 
 	set->tags = kmalloc_node(set->nr_hw_queues *