Re: [PATCH 1/2] block: Call .limit_depth() after .hctx has been set

[Christoph Hellwig <hch@lst.de>]

Calling limit_depth with the hctx set make sense, but the way it's done
looks odd.  Why not something like this?

diff --git a/block/blk-mq.c b/block/blk-mq.c
index b8dbfed8b28be1..88886fd93b1a9c 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -448,6 +448,10 @@ static struct request *__blk_mq_alloc_requests(struct blk_mq_alloc_data *data)
 	if (data->cmd_flags & REQ_NOWAIT)
 		data->flags |= BLK_MQ_REQ_NOWAIT;
 
+retry:
+	data->ctx = blk_mq_get_ctx(q);
+	data->hctx = blk_mq_map_queue(q, data->cmd_flags, data->ctx);
+
 	if (q->elevator) {
 		/*
 		 * All requests use scheduler tags when an I/O scheduler is
@@ -469,13 +473,9 @@ static struct request *__blk_mq_alloc_requests(struct blk_mq_alloc_data *data)
 			if (ops->limit_depth)
 				ops->limit_depth(data->cmd_flags, data);
 		}
-	}
-
-retry:
-	data->ctx = blk_mq_get_ctx(q);
-	data->hctx = blk_mq_map_queue(q, data->cmd_flags, data->ctx);
-	if (!(data->rq_flags & RQF_SCHED_TAGS))
+	} else {
 		blk_mq_tag_busy(data->hctx);
+	}
 
 	if (data->flags & BLK_MQ_REQ_RESERVED)
 		data->rq_flags |= RQF_RESV;