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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@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Arianna Avanzini <avanzini.arianna@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Tejun Heo 2015-08-18 14:55:19 -07:00 committed by Jens Axboe
parent 85b6bc9db6
commit c9589f03e4
1 changed files with 4 additions and 3 deletions
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7
block/blk-throttle.c
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@ -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) {