linux-kernel - Re: [PATCH V3 1/5] cpufreq: ondemand: Drop unnecessary locks from update_sampling

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Message-ID: <9152551.Va141R8GGE@vostro.rjw.lan>
Date:	Wed, 28 Oct 2015 05:05:06 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 1/5] cpufreq: ondemand: Drop unnecessary locks from update_sampling_rate()

On Tuesday, October 13, 2015 01:39:01 PM Viresh Kumar wrote:
> 'timer_mutex' is required to sync work-handlers of policy->cpus.
> update_sampling_rate() is just canceling the works and queuing them
> again. This isn't protecting anything at all in update_sampling_rate()
> and is not gonna be of any use.
> 
> Even if a work-handler is already running for a CPU,
> cancel_delayed_work_sync() will wait for it to finish.
> 
> Drop these unnecessary locks.
> 
> Reviewed-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>

I'm queuing this up for 4.4, although I think that the changelog is not right.

While at it, what are the race conditions the lock is protecting against?

Thanks,
Rafael

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