Re: od_set_powersave_bias: NULL pointer dereference

From: Tim Gardner <tim.gardner@canonical.com>
To: Jacob Shin <jacob.shin@amd.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>,
	"Rafael J. Wysocki" <rjw@sisk.pl>,
	LKML <linux-kernel@vger.kernel.org>,
	cpufreq@vger.kernel.org, linux-pm@vger.kernel.org
Subject: Re: od_set_powersave_bias: NULL pointer dereference
Date: Tue, 25 Jun 2013 12:41:07 -0600	[thread overview]
Message-ID: <51C9E443.8070100@canonical.com> (raw)
In-Reply-To: <20130625161935.GA10208@jshin-Toonie>

On 06/25/2013 10:19 AM, Jacob Shin wrote:
> On Tue, Jun 25, 2013 at 12:26:14PM +0530, Viresh Kumar wrote:
>> On 24 June 2013 22:29, Tim Gardner <tim.gardner@canonical.com> wrote:
>>> This is from Ubuntu Saucy based on 3.10-rc7:
>>>
>>> [   12.911676] BUG: unable to handle kernel NULL pointer dereference at
>>> 0000000000000070
>>> [   12.911691] IP: [<ffffffff8156e572>] od_set_powersave_bias+0x92/0xc0
>>>
>>
>> Can you please look into this bug? It occurred after your
>> patch... This is the boot log crash we have:
> 
> Hi,
> 
> Yes, so sorry about that, it looks like I failed to test with:
> 
> CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE=y
> CONFIG_CPU_FREQ_GOV_PERFORMANCE=y
> CONFIG_CPU_FREQ_GOV_ONDEMAND=y
> CONFIG_X86_AMD_FREQ_SENSITIVITY=m
> 
> The following patch fixes this, Tim, could you please test ? :
> 
> ---8<---
> 
> From 3c727b1f775448599e67c5fb2121d79448e80c90 Mon Sep 17 00:00:00 2001
> From: Jacob Shin <jacob.shin@amd.com>
> Date: Tue, 25 Jun 2013 10:40:54 -0500
> Subject: [PATCH 1/1] cpufreq: fix NULL pointer deference at
>  od_set_powersave_bias()
> 
> When initializing the default powersave_bias value, we need to first
> make sure that this policy is running the ondemand governor.
> 
> Reported-by: Tim Gardner <tim.gardner@canonical.com>
> Signed-off-by: Jacob Shin <jacob.shin@amd.com>
> ---
>  drivers/cpufreq/cpufreq_ondemand.c |   17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
> index 4b9bb5d..93eb5cb 100644
> --- a/drivers/cpufreq/cpufreq_ondemand.c
> +++ b/drivers/cpufreq/cpufreq_ondemand.c
> @@ -47,6 +47,8 @@ static struct od_ops od_ops;
>  static struct cpufreq_governor cpufreq_gov_ondemand;
>  #endif
>  
> +static unsigned int default_powersave_bias;
> +
>  static void ondemand_powersave_bias_init_cpu(int cpu)
>  {
>  	struct od_cpu_dbs_info_s *dbs_info = &per_cpu(od_cpu_dbs_info, cpu);
> @@ -543,7 +545,7 @@ static int od_init(struct dbs_data *dbs_data)
>  
>  	tuners->sampling_down_factor = DEF_SAMPLING_DOWN_FACTOR;
>  	tuners->ignore_nice = 0;
> -	tuners->powersave_bias = 0;
> +	tuners->powersave_bias = default_powersave_bias;
>  	tuners->io_is_busy = should_io_be_busy();
>  
>  	dbs_data->tuners = tuners;
> @@ -585,6 +587,7 @@ static void od_set_powersave_bias(unsigned int powersave_bias)
>  	unsigned int cpu;
>  	cpumask_t done;
>  
> +	default_powersave_bias = powersave_bias;
>  	cpumask_clear(&done);
>  
>  	get_online_cpus();
> @@ -593,11 +596,17 @@ static void od_set_powersave_bias(unsigned int powersave_bias)
>  			continue;
>  
>  		policy = per_cpu(od_cpu_dbs_info, cpu).cdbs.cur_policy;
> -		dbs_data = policy->governor_data;
> -		od_tuners = dbs_data->tuners;
> -		od_tuners->powersave_bias = powersave_bias;
> +		if (!policy)
> +			continue;
>  
>  		cpumask_or(&done, &done, policy->cpus);
> +
> +		if (policy->governor != &cpufreq_gov_ondemand)
> +			continue;
> +
> +		dbs_data = policy->governor_data;
> +		od_tuners = dbs_data->tuners;
> +		od_tuners->powersave_bias = default_powersave_bias;
>  	}
>  	put_online_cpus();
>  }
> 

That appears to have done the trick. You can add my Tested-by.

rtg

-- 
Tim Gardner tim.gardner@canonical.com