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Message-ID: <20221129030147.27400-4-shikemeng@huawei.com>
Date: Tue, 29 Nov 2022 11:01:40 +0800
From: Kemeng Shi <shikemeng@...wei.com>
To: <tj@...nel.org>, <josef@...icpanda.com>, <axboe@...nel.dk>
CC: <cgroups@...r.kernel.org>, <linux-block@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, <shikemeng@...wei.com>
Subject: [PATCH v2 03/10] 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.
Signed-off-by: Kemeng Shi <shikemeng@...wei.com>
Acked-by: Tejun Heo <tj@...nel.org>
---
block/blk-throttle.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index d516a37e82fb..ee7dc1a0adfd 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -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.
--
2.30.0
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