From: Yu Kuai <yukuai3@huawei.com>

Tightening the throttle activation check in blk_throtl_activated() to
require both q->td presence and policy bit set introduced a memory leak
during disk release:

blkg_destroy_all() clears the policy bit first during queue deactivation,
causing subsequent blk_throtl_exit() to skip throtl_data cleanup when
blk_throtl_activated() fails policy check.

Idealy we should avoid modifying blk_throtl_exit() activation check because
it's intuitive that blk-throtl start from blk_throtl_init() and end in
blk_throtl_exit(). However, call blk_throtl_exit() before
blkg_destroy_all() will make a long term deadlock problem easier to
trigger[1], hence fix this problem by checking if q->td is NULL from
blk_throtl_exit(), and remove policy deactivation as well since it's
useless.

[1] https://lore.kernel.org/all/CAHj4cs9p9H5yx+ywsb3CMUdbqGPhM+8tuBvhW=9ADiCjAqza9w@mail.gmail.com/#t
Fixes: bd9fd5be6bc0 ("blk-throttle: fix access race during throttle policy activation")
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Closes: https://lore.kernel.org/all/CAHj4cs-p-ZwBEKigBj7T6hQCOo-H68-kVwCrV6ZvRovrr9Z+HA@mail.gmail.com/
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
Changes in v2:
 - fix the problem by checking q->td directly;

 block/blk-throttle.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index f510ae072868..2c5b64b1a724 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -1842,12 +1842,15 @@ void blk_throtl_exit(struct gendisk *disk)
 {
 	struct request_queue *q = disk->queue;
 
-	if (!blk_throtl_activated(q))
+	/*
+	 * blkg_destroy_all() already deactivate throtl policy, just check and
+	 * free throtl data.
+	 */
+	if (!q->td)
 		return;
 
 	timer_delete_sync(&q->td->service_queue.pending_timer);
 	throtl_shutdown_wq(q);
-	blkcg_deactivate_policy(disk, &blkcg_policy_throtl);
 	kfree(q->td);
 }
 
-- 
2.39.2

On Wed, 17 Sep 2025 15:55:39 +0800, Yu Kuai wrote:
> Tightening the throttle activation check in blk_throtl_activated() to
> require both q->td presence and policy bit set introduced a memory leak
> during disk release:
> 
> blkg_destroy_all() clears the policy bit first during queue deactivation,
> causing subsequent blk_throtl_exit() to skip throtl_data cleanup when
> blk_throtl_activated() fails policy check.
> 
> [...]

Applied, thanks!

[1/1] blk-throttle: fix throtl_data leak during disk release
      (no commit info)

Best regards,
-- 
Jens Axboe