linux-kernel - Re: [PATCH 1/9] sched: Simplify get_nohz_timer

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAEXW_YSJ-G_zUKLzLgvCkxAY-dg_Zxo6n=bEXyeEmo9hEMcZpg@mail.gmail.com>
Date:   Sun, 6 Aug 2023 17:39:24 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/9] sched: Simplify get_nohz_timer_target()

On Sun, Aug 6, 2023 at 9:52 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> Use guards to reduce gotos and simplify control flow.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/sched/core.c |   15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1097,25 +1097,22 @@ int get_nohz_timer_target(void)
>
>         hk_mask = housekeeping_cpumask(HK_TYPE_TIMER);
>
> -       rcu_read_lock();
> +       guard(rcu)();
> +
>         for_each_domain(cpu, sd) {
>                 for_each_cpu_and(i, sched_domain_span(sd), hk_mask) {
>                         if (cpu == i)
>                                 continue;
>
> -                       if (!idle_cpu(i)) {
> -                               cpu = i;
> -                               goto unlock;
> -                       }
> +                       if (!idle_cpu(i))
> +                               return i;
>                 }
>         }
>
>         if (default_cpu == -1)
>                 default_cpu = housekeeping_any_cpu(HK_TYPE_TIMER);
> -       cpu = default_cpu;
> -unlock:
> -       rcu_read_unlock();
> -       return cpu;
> +
> +       return default_cpu;
>  }

Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>

I haven't looked into the actual implementation of the guard stuff,
but rcu_read_lock_guarded() is less of an eyesore to me than
guard(rcu)(); TBH.

thanks,

 - Joel