linux-kernel - Re: [PATCH v2 3/4] cpufreq: Fix governor module removal race

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Date:   Tue, 28 Nov 2017 08:08:12 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH v2 3/4] cpufreq: Fix governor module removal race

On 23-11-17, 14:27, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> It is possible to remove a cpufreq governor module after
> cpufreq_parse_governor() has returned success in
> store_scaling_governor() and before cpufreq_set_policy()
> acquires a reference to it, because the governor list is
> not protected during that period and nothing prevents the
> governor from being unregistered then.
> 
> Prevent that from happening by acquiring an extra reference
> to the governor module temporarily in cpufreq_parse_governor(),
> under cpufreq_governor_mutex, and dropping it in
> store_scaling_governor(), when cpufreq_set_policy() returns.
> 
> Note that the second cpufreq_parse_governor() call site is fine,
> because it only cares about the policy member of new_policy.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> 
> -> v2: Drop changes to clear policy->governor in
>        cpufreq_parse_governor() in the cpufreq_driver->setpolicy set
>        case, as that field should always be NULL then.
> 
> ---
>  drivers/cpufreq/cpufreq.c |    6 ++++++
>  1 file changed, 6 insertions(+)

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

-- 
viresh