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Message-ID: <3267506.5YnhcYthBi@vostro.rjw.lan>
Date: Thu, 10 Mar 2016 23:20:47 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Richard Cochran <rcochran@...utronix.de>
Cc: linux-kernel@...r.kernel.org, rt@...utronix.de,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
Viresh Kumar <viresh.kumar@...aro.org>,
Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: Make cpufreq_quick_get() safe to call.
On Thursday, March 10, 2016 04:10:36 PM Richard Cochran wrote:
> The function, cpufreq_quick_get, accesses the global 'cpufreq_driver' and
> its fields without taking the associated lock, cpufreq_driver_lock.
>
> Without the locking, nothing guarantees that 'cpufreq_driver' remains
> consistent during the call. This patch fixes the issue by taking the lock
> before accessing the data structure.
>
> Cc: Dirk Brandewie <dirk.brandewie@...il.com>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Signed-off-by: Richard Cochran <rcochran@...utronix.de>
Can you please CC PM-related patches to linux-pm@...r.kernel.org? They
are much easier to handle for me then.
> ---
> drivers/cpufreq/cpufreq.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index e979ec7..ce02b2b 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1457,9 +1457,17 @@ unsigned int cpufreq_quick_get(unsigned int cpu)
> {
> struct cpufreq_policy *policy;
> unsigned int ret_freq = 0;
> + unsigned long flags;
> +
> + read_lock_irqsave(&cpufreq_driver_lock, flags);
>
> if (cpufreq_driver && cpufreq_driver->setpolicy && cpufreq_driver->get)
> - return cpufreq_driver->get(cpu);
> + ret_freq = cpufreq_driver->get(cpu);
> +
> + read_unlock_irqrestore(&cpufreq_driver_lock, flags);
> +
> + if (ret_freq)
> + return ret_freq;
>
> policy = cpufreq_cpu_get(cpu);
> if (policy) {
>
I would prefer something like this:
read_lock_irqsave(&cpufreq_driver_lock, flags);
if (cpufreq_driver && cpufreq_driver->setpolicy && cpufreq_driver->get) {
unsigned int ret_freq = cpufreq_driver->get(cpu);
read_unlock_irqrestore(&cpufreq_driver_lock, flags);
return ret_freq;
}
read_unlock_irqrestore(&cpufreq_driver_lock, flags);
Thanks,
Rafael
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