Re: [PATCH v3 1/5] arch_topology: validate input frequencies to arch_set_freq_scale()

From: Viresh Kumar <viresh.kumar@linaro.org>
To: Ionela Voinescu <ionela.voinescu@arm.com>
Cc: rjw@rjwysocki.net, dietmar.eggemann@arm.com,
	catalin.marinas@arm.com, sudeep.holla@arm.com, will@kernel.org,
	valentin.schneider@arm.com, linux-pm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/5] arch_topology: validate input frequencies to arch_set_freq_scale()
Date: Tue, 25 Aug 2020 11:26:18 +0530	[thread overview]
Message-ID: <20200825055618.ybght3enlpuwo3va@vireshk-i7> (raw)
In-Reply-To: <20200824210252.27486-2-ionela.voinescu@arm.com>

On 24-08-20, 22:02, Ionela Voinescu wrote:
> The current frequency passed to arch_set_freq_scale() could end up
> being 0, signaling an error in setting a new frequency. Also, if the
> maximum frequency in 0, this will result in a division by 0 error.
> 
> Therefore, validate these input values before using them for the
> setting of the frequency scale factor.
> 
> Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
> Cc: Sudeep Holla <sudeep.holla@arm.com>
> Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
> ---
>  drivers/base/arch_topology.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index 75f72d684294..1aca82fcceb8 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -33,6 +33,9 @@ void arch_set_freq_scale(struct cpumask *cpus, unsigned long cur_freq,
>  	unsigned long scale;
>  	int i;
>  
> +	if (!cur_freq || !max_freq)

We should probably use unlikely() here.

Rafael: Shouldn't this have a WARN_ON_ONCE() as well ?

> +		return;
> +
>  	/*
>  	 * If the use of counters for FIE is enabled, just return as we don't
>  	 * want to update the scale factor with information from CPUFREQ.
> -- 
> 2.17.1

-- 
viresh