在 2021/12/02 22:48, Michal Koutný 写道:
Hello Kuai.
On Thu, Dec 02, 2021 at 09:04:40PM +0800, Yu Kuai <yukuai3@xxxxxxxxxx> wrote:
For example, if user thread is throttled with low bps while it's
issuing large io, and the device is deleted. The user thread will
wait for a long time for io to return.
Do I understand correctly the "long time" here is
outstanding_IO_size/throttled_bandwidth? Or are you getting at some
Hi, Michal
Yes, this is exactly what I mean.
other cause/longer time?
+void blk_throtl_cancel_bios(struct request_queue *q)
+{
+ struct throtl_data *td = q->td;
+ struct bio_list bio_list_on_stack;
+ struct blkcg_gq *blkg;
+ struct cgroup_subsys_state *pos_css;
+ struct bio *bio;
+ int rw;
+
+ bio_list_init(&bio_list_on_stack);
+
+ /*
+ * hold queue_lock to prevent concurrent with dispatching
+ * throttled bios by timer.
+ */
+ spin_lock_irq(&q->queue_lock);
You've replaced the rcu_read_lock() with the queue lock but...
+
+ /*
+ * Drain each tg while doing post-order walk on the blkg tree, so
+ * that all bios are propagated to td->service_queue. It'd be
+ * better to walk service_queue tree directly but blkg walk is
+ * easier.
+ */
+ blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg)
+ tg_drain_bios(&blkg_to_tg(blkg)->service_queue);
...you also need the rcu_read_lock() here since you may encounter a
(descendant) blkcg that's removed concurrently.
blkg_destroy() is protected by the queue_lock，so I think queue_lock can
protect such concurrent scenario.
Thanks,
Kuai
(I may miss some consequences of doing this under the queue_lock so if
the concurrent removal is ruled out, please make a comment about it.)
Regards,
Michal
