block: Provide blk_mq_sched_get_icq()

Currently we lookup ICQ only after the request is allocated. However BFQ
will want to decide how many scheduler tags it allows a given bfq queue
(effectively a process) to consume based on cgroup weight. So provide a
function blk_mq_sched_get_icq() so that BFQ can lookup ICQ earlier.
Acked-by: NPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: NJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20211125133645.27483-1-jack@suse.czSigned-off-by: NJens Axboe <axboe@kernel.dk>

block/blk-mq-sched.c

@@ -18,9 +18,8 @@
 #include "blk-mq-tag.h"
 #include "blk-wbt.h"
 
-void blk_mq_sched_assign_ioc(struct request *rq)
+struct io_cq *blk_mq_sched_get_icq(struct request_queue *q)
 {
-	struct request_queue *q = rq->q;
 	struct io_context *ioc;
 	struct io_cq *icq;
 
@@ -28,22 +27,27 @@ void blk_mq_sched_assign_ioc(struct request *rq)
 	if (unlikely(!current->io_context))
 		create_task_io_context(current, GFP_ATOMIC, q->node);
 
-	/*
-	 * May not have an IO context if it's a passthrough request
-	 */
+	/* May not have an IO context if context creation failed */
 	ioc = current->io_context;
 	if (!ioc)
-		return;
+		return NULL;
 
 	spin_lock_irq(&q->queue_lock);
 	icq = ioc_lookup_icq(ioc, q);
 	spin_unlock_irq(&q->queue_lock);
+	if (icq)
+		return icq;
+	return ioc_create_icq(ioc, q, GFP_ATOMIC);
+}
+EXPORT_SYMBOL(blk_mq_sched_get_icq);
 
-	if (!icq) {
-		icq = ioc_create_icq(ioc, q, GFP_ATOMIC);
-		if (!icq)
-			return;
-	}
+void blk_mq_sched_assign_ioc(struct request *rq)
+{
+	struct io_cq *icq;
+
+	icq = blk_mq_sched_get_icq(rq->q);
+	if (!icq)
+		return;
 	get_io_context(icq->ioc);
 	rq->elv.icq = icq;
 }

block/blk-mq-sched.h

@@ -8,6 +8,7 @@
 
 #define MAX_SCHED_RQ (16 * BLKDEV_DEFAULT_RQ)
 
+struct io_cq *blk_mq_sched_get_icq(struct request_queue *q);
 void blk_mq_sched_assign_ioc(struct request *rq);
 
 bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,