linux-kernel - Re: [PATCH] cpufreq: amd-pstate: avoid uninitialized variable use

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Date:   Wed, 8 Feb 2023 14:28:24 +0000
From:   Wyes Karny <wyes.karny@....com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Huang Rui <ray.huang@....com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Perry Yuan <Perry.Yuan@....com>,
        Mario Limonciello <Mario.Limonciello@....com>,
        Arnd Bergmann <arnd@...db.de>, Jinzhou Su <Jinzhou.Su@....com>,
        Meng Li <li.meng@....com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: amd-pstate: avoid uninitialized variable use

On 07 Feb 17:12, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> The new epp support causes warnings about three separate
> but related bugs:
> 
> 1) failing before allocation should just return an error:
> 
> drivers/cpufreq/amd-pstate.c:951:6: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (!dev)
>             ^~~~
> drivers/cpufreq/amd-pstate.c:1018:9: note: uninitialized use occurs here
>         return ret;
>                ^~~
> 
> 2) wrong variable to store return code:
> 
> drivers/cpufreq/amd-pstate.c:963:6: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (rc)
>             ^~
> drivers/cpufreq/amd-pstate.c:1019:9: note: uninitialized use occurs here
>         return ret;
>                ^~~
> drivers/cpufreq/amd-pstate.c:963:2: note: remove the 'if' if its condition is always false
>         if (rc)
>         ^~~~~~~
> 
> 3) calling amd_pstate_set_epp() in cleanup path after determining
> that it should not be called:
> 
> drivers/cpufreq/amd-pstate.c:1055:6: error: variable 'epp' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (cpudata->epp_policy == cpudata->policy)
>             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/cpufreq/amd-pstate.c:1080:30: note: uninitialized use occurs here
>         amd_pstate_set_epp(cpudata, epp);
>                                     ^~~
> 
> All three are trivial to fix, but most likely there are additional bugs
> in this function when the error handling was not really tested.
> 
> Fixes: ffa5096a7c33 ("cpufreq: amd-pstate: implement Pstate EPP support for the AMD processors")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/cpufreq/amd-pstate.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 168a28bed6ee..847f5f31396d 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -940,7 +940,6 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>  	int min_freq, max_freq, nominal_freq, lowest_nonlinear_freq, ret;
>  	struct amd_cpudata *cpudata;
>  	struct device *dev;
> -	int rc;
>  	u64 value;
>  
>  	/*
> @@ -950,7 +949,7 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>  	amd_perf_ctl_reset(policy->cpu);
>  	dev = get_cpu_device(policy->cpu);
>  	if (!dev)
> -		goto free_cpudata1;
> +		return -ENODEV;
>  
>  	cpudata = kzalloc(sizeof(*cpudata), GFP_KERNEL);
>  	if (!cpudata)
> @@ -959,8 +958,8 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>  	cpudata->cpu = policy->cpu;
>  	cpudata->epp_policy = 0;
>  
> -	rc = amd_pstate_init_perf(cpudata);
> -	if (rc)
> +	ret = amd_pstate_init_perf(cpudata);
> +	if (ret)
>  		goto free_cpudata1;
>  
>  	min_freq = amd_get_min_freq(cpudata);
> @@ -1076,9 +1075,9 @@ static void amd_pstate_epp_init(unsigned int cpu)
>  		value |= (u64)epp << 24;
>  	}
>  
> +	amd_pstate_set_epp(cpudata, epp);
>  skip_epp:
>  	WRITE_ONCE(cpudata->cppc_req_cached, value);
> -	amd_pstate_set_epp(cpudata, epp);
>  	cpufreq_cpu_put(policy);
>  }
> 

Tested this on AMD Milan (Zen 3) system.

Tested-by: Wyes Karny <wyes.karny@....com>

> -- 
> 2.39.1
>