linux-kernel - [PATCH] blk-iocost: do not WARNING if iocg has already offlined

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Date: Thu, 18 Apr 2024 15:23:40 +0800
From: linan666@...weicloud.com
To: tj@...nel.org,
	josef@...icpanda.com,
	axboe@...nel.dk
Cc: hch@....de,
	cgroups@...r.kernel.org,
	linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linan666@...weicloud.com,
	yukuai3@...wei.com,
	yi.zhang@...wei.com,
	houtao1@...wei.com,
	yangerkun@...wei.com
Subject: [PATCH] blk-iocost: do not WARNING if iocg has already offlined

From: Li Nan <linan122@...wei.com>

In iocg_pay_debt(), warn is triggered if 'active_list' is empty, which
is intended to confirm iocg is avitve when it has debt. However, warn
can be triggered during removing cgroup controller, as
iocg_waitq_timer_fn() is awakened at that time.

  WARNING: CPU: 0 PID: 2344971 at block/blk-iocost.c:1402 iocg_pay_debt+0x14c/0x190
  Call trace:
  iocg_pay_debt+0x14c/0x190
  iocg_kick_waitq+0x438/0x4c0
  iocg_waitq_timer_fn+0xd8/0x130
  __run_hrtimer+0x144/0x45c
  __hrtimer_run_queues+0x16c/0x244
  hrtimer_interrupt+0x2cc/0x7b0

The warn in this situation is meaningless. Since this iocg is being
removed, the state of the 'active_list' is irrelevant, and 'waitq_timer'
is canceled after removing 'active_list' in ioc_pd_free(), which ensure
iocg is freed after iocg_waitq_timer_fn() returns.

Therefore, add the check if iocg has already offlined to avoid warn
when removing cgroup controller.

Signed-off-by: Li Nan <linan122@...wei.com>
---
 block/blk-iocost.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index baa20c85799d..2e109c016a39 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -1440,7 +1440,7 @@ static void iocg_pay_debt(struct ioc_gq *iocg, u64 abs_vpay,
 	lockdep_assert_held(&iocg->waitq.lock);

 	/* make sure that nobody messed with @iocg */
-	WARN_ON_ONCE(list_empty(&iocg->active_list));
+	WARN_ON_ONCE(list_empty(&iocg->active_list) && iocg->pd.online);
 	WARN_ON_ONCE(iocg->inuse > 1);

 	iocg->abs_vdebt -= min(abs_vpay, iocg->abs_vdebt);
-- 
2.39.2