From: "Rafael J. Wysocki" <rafael@kernel.org>
To: "Joel Fernandes (Google)" <joelaf@google.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"Joel Fernandes (Google)" <joel@joelfernandes.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Patrick Bellasi <patrick.bellasi@arm.com>,
Juri Lelli <juri.lelli@redhat.com>,
Luca Abeni <luca.abeni@santannapisa.it>,
Todd Kjos <tkjos@google.com>,
Claudio Scordino <claudio@evidence.eu.com>,
kernel-team@android.com, Linux PM <linux-pm@vger.kernel.org>
Subject: Re: [PATCH RFC] schedutil: Address the r/w ordering race in kthread
Date: Wed, 23 May 2018 10:23:56 +0200 [thread overview]
Message-ID: <CAJZ5v0hKB7s52K+=0Gk-_10tLzORN+VXnJuVe9odyEdwgK-PnQ@mail.gmail.com> (raw)
In-Reply-To: <20180522235028.80564-1-joel@joelfernandes.org>
On Wed, May 23, 2018 at 1:50 AM, Joel Fernandes (Google)
<joelaf@google.com> wrote:
> Currently there is a race in schedutil code for slow-switch single-CPU
> systems. Fix it by enforcing ordering the write to work_in_progress to
> happen before the read of next_freq.
>
> Kthread Sched update
>
> sugov_work() sugov_update_single()
>
> lock();
> // The CPU is free to rearrange below
> // two in any order, so it may clear
> // the flag first and then read next
> // freq. Lets assume it does.
> work_in_progress = false
>
> if (work_in_progress)
> return;
>
> sg_policy->next_freq = 0;
> freq = sg_policy->next_freq;
> sg_policy->next_freq = real-freq;
> unlock();
>
> Reported-by: Viresh Kumar <viresh.kumar@linaro.org>
> CC: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> CC: Peter Zijlstra <peterz@infradead.org>
> CC: Ingo Molnar <mingo@redhat.com>
> CC: Patrick Bellasi <patrick.bellasi@arm.com>
> CC: Juri Lelli <juri.lelli@redhat.com>
> Cc: Luca Abeni <luca.abeni@santannapisa.it>
> CC: Todd Kjos <tkjos@google.com>
> CC: claudio@evidence.eu.com
> CC: kernel-team@android.com
> CC: linux-pm@vger.kernel.org
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> ---
> I split this into separate patch, because this race can also happen in
> mainline.
>
> kernel/sched/cpufreq_schedutil.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 5c482ec38610..ce7749da7a44 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -401,6 +401,13 @@ static void sugov_work(struct kthread_work *work)
> */
> raw_spin_lock_irqsave(&sg_policy->update_lock, flags);
> freq = sg_policy->next_freq;
> +
> + /*
> + * sugov_update_single can access work_in_progress without update_lock,
> + * make sure next_freq is read before work_in_progress is set.
> + */
> + smp_mb();
> +
This requires a corresponding barrier somewhere else.
> sg_policy->work_in_progress = false;
> raw_spin_unlock_irqrestore(&sg_policy->update_lock, flags);
>
> --
Also, as I said I actually would prefer to use the spinlock in the
one-CPU case when the kthread is used.
I'll have a patch for that shortly.
prev parent reply other threads:[~2018-05-23 8:23 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-22 23:50 [PATCH RFC] schedutil: Address the r/w ordering race in kthread Joel Fernandes (Google)
2018-05-23 0:18 ` Joel Fernandes
2018-05-23 6:47 ` Juri Lelli
2018-05-23 8:23 ` Rafael J. Wysocki [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAJZ5v0hKB7s52K+=0Gk-_10tLzORN+VXnJuVe9odyEdwgK-PnQ@mail.gmail.com' \
--to=rafael@kernel.org \
--cc=claudio@evidence.eu.com \
--cc=joel@joelfernandes.org \
--cc=joelaf@google.com \
--cc=juri.lelli@redhat.com \
--cc=kernel-team@android.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pm@vger.kernel.org \
--cc=luca.abeni@santannapisa.it \
--cc=mingo@redhat.com \
--cc=patrick.bellasi@arm.com \
--cc=peterz@infradead.org \
--cc=rafael.j.wysocki@intel.com \
--cc=tkjos@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).