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blk-throttle: ignore cgroup without io queued in blk_throtl_cancel_bios

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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>
This commit is contained in:
Kemeng Shi 2022-12-05 19:57:03 +08:00 committed by Jens Axboe
parent 84aca0a7e0
commit eb18479182
1 changed files with 12 additions and 1 deletions
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13
block/blk-throttle.c
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@ -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.