linux-kernel - Re: [PATCH v2] schedutil: Allow cpufreq requests to be made even when kthread kicked

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]

Date:   Tue, 22 May 2018 16:26:24 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     "Joel Fernandes (Google.)" <joelaf@...gle.com>,
        linux-kernel@...r.kernel.org,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Todd Kjos <tkjos@...gle.com>, claudio@...dence.eu.com,
        kernel-team@...roid.com, linux-pm@...r.kernel.org
Subject: Re: [PATCH v2] schedutil: Allow cpufreq requests to be made even
 when kthread kicked

On 22-05-18, 11:51, Patrick Bellasi wrote:
> It could happen, but using:
> 
>    raw_spin_lock_irqsave(&sg_policy->update_lock, flags);
>    freq = READ_ONCE(sg_policy->next_freq)
>    WRITE_ONCE(sg_policy->work_in_progress, false);
>    raw_spin_unlock_irqrestore(&sg_policy->update_lock, flags);
> 
>                        if (!READ_ONCE(sg_policy->work_in_progress)) {
>                            WRITE_ONCE(sg_policy->work_in_progress, true);
>                            irq_work_queue(&sg_policy->irq_work);
>                        }

I think its better to get locking in place for non-fast switching case in
single-policy systems right now.

> should fix it by enforcing the ordering as well as documenting the
> concurrent access.
> 
> However, in the "sched update" side, where do we have the sequence:
> 
>    sg_policy->next_freq = 0;
>    sg_policy->next_freq = real-next-freq;

Ah, that was just an example of what a compiler may do (though it shouldn't do).

-- 
viresh