Re: [PATCH 3/4] block: move queue enter logic into blk_mq_submit_bio()

On Thu, Nov 04, 2021 at 05:41:35AM -0600, Jens Axboe wrote:

quoted

quoted

 	if (!submit_bio_checks(bio) || !blk_crypto_bio_prep(&bio))
-		goto queue_exit;
+		return;

This is broken, we really ant the submit checks under freeze
protection to make sure the parameters can't be changed underneath
us.

Which parameters are you worried about in submit_bio_checks()? I don't
immediately see anything that would make me worry about it.

Mostly checks if certain operations are supported or not, as
revalidation could clear those.

quoted

This looks weird, as blk_try_enter_queue is already called by
bio_queue_enter.

It's just for avoiding a pointless call into bio_queue_enter(), which
isn't needed it blk_try_enter_queue() is successful. The latter is short
and small and can be inlined, while bio_queue_enter() is a lot bigger.

If this is so impotant let's operated with an inlined bio_queue_enter
that calls out of line into slow path instead of open coding it
like this.

quoted

quoted

 	} else {
 		struct blk_mq_alloc_data data = {
 			.q		= q,

@@ -2528,6 +2534,11 @@ void blk_mq_submit_bio(struct bio *bio)
 			.cmd_flags	= bio->bi_opf,
 		};
 
+		if (unlikely(!blk_mq_queue_enter(q, bio)))
+			return;
+
+		rq_qos_throttle(q, bio);
+

At some point the code in this !cached branch really needs to move
into a helper..

Like in the next patch?

No, I mean the !cached case which is a lot more convoluted.