linux-kernel - Re: [PATCH v2 5/8] sched,x86: Enable Turbo Boost Max Technology

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Date:   Thu, 08 Sep 2016 23:22 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>, tglx@...utronix.de,
        mingo@...hat.com, bp@...e.de, x86@...nel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org
Subject: Re: [PATCH v2 5/8] sched,x86: Enable Turbo Boost Max Technology

On Thursday, September 08, 2016 11:28:48 AM Srinivas Pandruvada wrote:
> On Thu, 2016-09-08 at 20:22 +0200, Peter Zijlstra wrote:
> > On Thu, Sep 08, 2016 at 11:09:28AM -0700, Tim Chen wrote:
> > > 
> > > On Thu, Sep 08, 2016 at 09:59:55AM +0200, Peter Zijlstra wrote:
> > > > 
> > > > I think there's a race here, if two tasks were to write to the
> > > > sysctl
> > > > they'd both change the value before getting stuck on the mutex in
> > > > enable_sched_itmt().
> > > > 
> > > > One way around that is doing something like:
> > > > 
> > > > 
> > > > 	struct ctl_table t;
> > > > 	int val = sysctl_sched_itmt_enabled;
> > > > 
> > > > 	t = *table;
> > > > 	t.data = &val;
> > > > 
> > > > 	proc_dointvec_minmax(&t, ...);
> > > > 
> > > > 	/* and update the sysctl_sched_itmt_enabled value inside the
> > > > mutex */
> > > > 	enable_sched_itmi(val);
> > > 
> > > Peter,
> > > 
> > > Since enable_sched_itmt is only used by sched_itmt_update_handler,
> > > I've moved the mutex locking to sched_itmt_update_handler to
> > > eliminate
> > > the race condition in the code path you mentioned.
> > 
> > That is indeed simpler. Thanks!
> Do we need to send v3 to include these changes?

Yes, please.

Thanks,
Rafael