Re: [PATCH v2] block/blk-iocost: read ioc_pd_stat params inside ioc->lock

[Tejun Heo <tj@kernel.org>]

On Mon, Aug 03, 2026 at 09:22:01PM +0800, Tao Cui wrote:
> @@ -3092,9 +3092,12 @@ static void ioc_pd_stat(struct blkg_policy_data *pd, struct seq_file *s)
>  {
>  	struct ioc_gq *iocg = pd_to_iocg(pd);
>  	struct ioc *ioc = iocg->ioc;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&ioc->lock, flags);
>  
>  	if (!ioc->enabled)
> -		return;
> +		goto out;
>  
>  	if (iocg->level == 0) {
>  		unsigned vp10k = DIV64_U64_ROUND_CLOSEST(
> @@ -3110,6 +3113,8 @@ static void ioc_pd_stat(struct blkg_policy_data *pd, struct seq_file *s)
>  			iocg->last_stat.wait_us,
>  			iocg->last_stat.indebt_us,
>  			iocg->last_stat.indelay_us);
> +out:
> +	spin_unlock_irqrestore(&ioc->lock, flags);
>  }

There's nothing in this function that requires synchronized reads. Might as
well just annotate them with data_race(). Otherwise, this can lead to a lot
of lock operations when there are a lot of cgroups and high frequency stat
reads.

Thanks.

-- 
tejun