Commit eb184791 authored Dec 05, 2022 by Kemeng Shi Committed by Jens Axboe Dec 05, 2022

blk-throttle: ignore cgroup without io queued in blk_throtl_cancel_bios



Ignore cgroup without io queued in blk_throtl_cancel_bios for two
reasons:
1. Save cpu cycle for trying to dispatch cgroup which is no io queued.
2. Avoid non-consistent state that cgroup is inserted to service queue
without THROTL_TG_PENDING set as tg_update_disptime will unconditional
re-insert cgroup to service queue. If we are on the default hierarchy,
IO dispatched from child in tg_dispatch_one_bio will trigger inserting
cgroup to service queue without erase first and ruin the tree.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Kemeng Shi <shikemeng@huawei.com>
Link: https://lore.kernel.org/r/20221205115709.251489-4-shikemeng@huaweicloud.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 84aca0a7

block/blk-throttle.c

+12 −1

Original line number	Diff line number	Diff line
		@@ -1738,7 +1738,18 @@ void blk_throtl_cancel_bios(struct gendisk *disk)
		* Set the flag to make sure throtl_pending_timer_fn() won't
		* stop until all throttled bios are dispatched.
		*/
		blkg_to_tg(blkg)->flags \|= THROTL_TG_CANCELING;
		tg->flags \|= THROTL_TG_CANCELING;

		/*
		* Do not dispatch cgroup without THROTL_TG_PENDING or cgroup
		* will be inserted to service queue without THROTL_TG_PENDING
		* set in tg_update_disptime below. Then IO dispatched from
		* child in tg_dispatch_one_bio will trigger double insertion
		* and corrupt the tree.
		*/
		if (!(tg->flags & THROTL_TG_PENDING))
		continue;

		/*
		* Update disptime after setting the above flag to make sure
		* throtl_select_dispatch() won't exit without dispatching.