linux-kernel - [PATCH 04/10] blk-throttle: improve queue bypass handling

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Date:	Sun, 12 Jul 2015 14:00:37 -0400
From:	Tejun Heo <tj@...nel.org>
To:	axboe@...nel.dk
Cc:	linux-kernel@...r.kernel.org, kernel-team@...com,
	vgoyal@...hat.com, avanzini.arianna@...il.com,
	Tejun Heo <tj@...nel.org>
Subject: [PATCH 04/10] blk-throttle: improve queue bypass handling

If a queue is bypassing, all blkcg policies should become noops but
blk-throttle wasn't.  It only became noop if the queue was dying.
While this wouldn't lead to an oops as falling back to the root blkg
is safe in this case, this can be a bit surprising - a bypassing queue
could still be applying throttle limits.

Fix it by removing blk_queue_dying() test in throtl_lookup_create_tg()
and testing blk_queue_bypass() in blk_throtl_bio() and bypassing
before doing anything else.

Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: Vivek Goyal <vgoyal@...hat.com>
Cc: Arianna Avanzini <avanzini.arianna@...il.com>
---
 block/blk-throttle.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 1f63fc8..900a777 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -475,7 +475,7 @@ static struct throtl_grp *throtl_lookup_create_tg(struct throtl_data *td,
 		/* if %NULL and @q is alive, fall back to root_tg */
 		if (!IS_ERR(blkg))
 			tg = blkg_to_tg(blkg);
-		else if (!blk_queue_dying(q))
+		else
 			tg = td_root_tg(td);
 	}
 
@@ -1438,10 +1438,11 @@ bool blk_throtl_bio(struct request_queue *q, struct bio *bio)
 	 * IO group
 	 */
 	spin_lock_irq(q->queue_lock);
-	tg = throtl_lookup_create_tg(td, blkcg);
-	if (unlikely(!tg))
+
+	if (unlikely(blk_queue_bypass(q)))
 		goto out_unlock;
 
+	tg = throtl_lookup_create_tg(td, blkcg);
 	sq = &tg->service_queue;
 
 	while (true) {
-- 
2.4.3

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