[PATCH v3 3/9] blk-throttle: ignore cgroup without io queued in blk_throtl_cancel_bios
From: Kemeng Shi
Date: Sun Dec 04 2022 - 22:58:14 EST
From: Kemeng Shi <shikemeng@xxxxxxxxxx>
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@xxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
---
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 2444ebf5f11d..75010110d481 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