block: move io_context creation into where it's needed

The only user of the io_context for IO is BFQ, yet we put the checking
and logic of it into the normal IO path.

Put the creation into blk_mq_sched_assign_ioc(), and have BFQ use that
helper.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bfq-iosched.c

@@ -6573,6 +6573,8 @@ static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd,
  */
 static void bfq_prepare_request(struct request *rq)
 {
+	blk_mq_sched_assign_ioc(rq);
+
 	/*
 	 * Regardless of whether we have an icq attached, we have to
 	 * clear the scheduler pointers, as they might point to

block/blk-core.c

@@ -750,15 +750,6 @@ noinline_for_stack bool submit_bio_checks(struct bio *bio)
 		break;
 	}
 
-	/*
-	 * Various block parts want %current->io_context, so allocate it up
-	 * front rather than dealing with lots of pain to allocate it only
-	 * where needed. This may fail and the block layer knows how to live
-	 * with it.
-	 */
-	if (unlikely(!current->io_context))
-		create_task_io_context(current, GFP_ATOMIC, q->node);
-
 	if (blk_throtl_bio(bio))
 		return false;
 

block/blk-mq-sched.c

@@ -24,6 +24,10 @@ void blk_mq_sched_assign_ioc(struct request *rq)
 	struct io_context *ioc;
 	struct io_cq *icq;
 
+	/* create task io_context, if we don't have one already */
+	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
 	 */
@@ -43,6 +47,7 @@ void blk_mq_sched_assign_ioc(struct request *rq)
 	get_io_context(icq->ioc);
 	rq->elv.icq = icq;
 }
+EXPORT_SYMBOL_GPL(blk_mq_sched_assign_ioc);
 
 /*
  * Mark a hardware queue as needing a restart. For shared queues, maintain

block/blk-mq.c

@@ -406,9 +406,6 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
 
 		if (!op_is_flush(data->cmd_flags) &&
 		    e->type->ops.prepare_request) {
-			if (e->type->icq_cache)
-				blk_mq_sched_assign_ioc(rq);
-
 			e->type->ops.prepare_request(rq);
 			rq->rq_flags |= RQF_ELVPRIV;
 		}