[Devel] [PATCH hci-8.1 2/2] ms/blk-throttle: fix throtl_data leak during disk release

["Denis V. Lunev" <den@openvz.org>]

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>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
(cherry picked from commit 336aec7b06be860477be80a4299263a2e9355789)

https://virtuozzo.atlassian.net/browse/VSTOR-152993
Feature: fix ms/block

Signed-off-by: Denis V. Lunev <den@openvz.org>
---
 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 cfa1cd60d2c5..95bf175c2a13 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);
 }
 
-- 
2.53.0

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