linux-kernel - Re: [PATCH V4] cpufreq: governor: Quit work-handlers early if governor is stopped

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Date:	Thu, 05 Nov 2015 23:41:36 +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,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V4] cpufreq: governor: Quit work-handlers early if governor is stopped

On Thursday, October 29, 2015 08:08:38 AM Viresh Kumar wrote:
> gov_queue_work() acquires cpufreq_governor_lock to allow
> cpufreq_governor_stop() to drain delayed work items possibly scheduled
> on CPUs that share the policy with a CPU being taken offline.
> 
> However, the same goal may be achieved in a more straightforward way if
> the policy pointer in the struct cpu_dbs_info matching the policy CPU is
> reset upfront by cpufreq_governor_stop() under the timer_mutex belonging
> to it and checked against NULL, under the same lock, at the beginning of
> dbs_timer().
> 
> In that case every instance of dbs_timer() run for a struct cpu_dbs_info
> sharing the policy pointer in question after cpufreq_governor_stop() has
> started will notice that that pointer is NULL and bail out immediately
> without queuing up any new work items.  In turn, gov_cancel_work()
> called by cpufreq_governor_stop() before destroying timer_mutex will
> wait for all of the delayed work items currently running on the CPUs
> sharing the policy to drop the mutex, so it may be destroyed safely.
> 
> Make cpufreq_governor_stop() and dbs_timer() work as described and
> modify gov_queue_work() so it does not acquire cpufreq_governor_lock any
> more.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>

Applied, thanks!

Rafael

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