linux-kernel - Re: [PATCH v3 09/57] sched: Simplify ttwu()

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Message-ID: <0012d943-6fd0-4b8d-9ec6-3d02aba75dcc@kadam.mountain>
Date:   Mon, 12 Jun 2023 16:51:17 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
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Subject: Re: [PATCH v3 09/57] sched: Simplify ttwu()

On Mon, Jun 12, 2023 at 11:07:22AM +0200, Peter Zijlstra wrote:
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3664,16 +3664,15 @@ ttwu_stat(struct task_struct *p, int cpu
>  		__schedstat_inc(p->stats.nr_wakeups_local);
>  	} else {
>  		struct sched_domain *sd;
> +		guard(rcu)();
>  
>  		__schedstat_inc(p->stats.nr_wakeups_remote);
> -		rcu_read_lock();

We can't put the guard(rcu)(); here?  I have unpublished static analysis
which assumes that the first and last statements guarded by a lock are
important.  But if we always put it at the top of the scope then we
lose that information.

>  		for_each_domain(rq->cpu, sd) {
>  			if (cpumask_test_cpu(cpu, sched_domain_span(sd))) {
>  				__schedstat_inc(sd->ttwu_wake_remote);
>  				break;
>  			}
>  		}
> -		rcu_read_unlock();
>  	}

regards,
dan carpenter