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>

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 1f63fc834dc3e6dab428ead1a0daee3b56574059..900a777e01c26a511fca0230d7c0f9edf4fb3111 100644 (file)
--- 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) {