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

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

[linan666]

From: Li Nan <linan122@huawei.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@huawei.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

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

[Yu Kuai]

在 2024/04/18 15:23, linan666@huaweicloud.com 写道:
> From: Li Nan <linan122@huawei.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

This line doesn't match the code from mainline, please mention that
which kernel release you're testing.

Other than that, ioc_pd_free() indeed clear 'active_list' before
canceling the timer, this patch looks good to me.

Reviewed-by: Yu Kuai <yukuai3@huawei.com>
>    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@huawei.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);
> 

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

[Li Nan]

在 2024/4/18 16:52, Yu Kuai 写道:
> 
> 
> 在 2024/04/18 15:23, linan666@huaweicloud.com 写道:
>> From: Li Nan <linan122@huawei.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
> 
> This line doesn't match the code from mainline, please mention that
> which kernel release you're testing.
> 

Thanks for your review.
I tested at 5.10, but mainline has the same issue.

> Other than that, ioc_pd_free() indeed clear 'active_list' before
> canceling the timer, this patch looks good to me.
> 
> Reviewed-by: Yu Kuai <yukuai3@huawei.com>

-- 
Thanks,
Nan

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

[Tejun Heo]

Hello,

On Thu, Apr 18, 2024 at 03:23:40PM +0800, linan666@huaweicloud.com wrote:
> From: Li Nan <linan122@huawei.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

Maybe saying "a blkcg is being removed" is clearer?

> 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@huawei.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);

Can you add a comment explaining why we need the pd.online test?

Other than the above nits, looks great to me. Please feel free to add

  Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun

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

[Li Nan]

在 2024/4/19 0:14, Tejun Heo 写道:
> Hello,
> 
> On Thu, Apr 18, 2024 at 03:23:40PM +0800, linan666@huaweicloud.com wrote:
>> From: Li Nan <linan122@huawei.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
> 
> Maybe saying "a blkcg is being removed" is clearer?

Thanks for your suggestion. I will correct my expression in next version.

> 
>> 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@huawei.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);
> 
> Can you add a comment explaining why we need the pd.online test?

Yeah, I will add comment in next version.

> 
> Other than the above nits, looks great to me. Please feel free to add
> 
>    Acked-by: Tejun Heo <tj@kernel.org>
> 
> Thanks.
> 

-- 
Thanks,
Nan