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SubjectRE: [PATCH] cpufreq: amd-pstate: avoid uninitialized variable use
Date
[AMD Official Use Only - General]

Hi Arnd,

> -----Original Message-----
> From: Arnd Bergmann <arnd@kernel.org>
> Sent: Wednesday, February 8, 2023 12:13 AM
> To: Huang, Ray <Ray.Huang@amd.com>; Rafael J. Wysocki
> <rafael@kernel.org>; Viresh Kumar <viresh.kumar@linaro.org>; Karny, Wyes
> <Wyes.Karny@amd.com>; Yuan, Perry <Perry.Yuan@amd.com>; Limonciello,
> Mario <Mario.Limonciello@amd.com>
> Cc: Arnd Bergmann <arnd@arndb.de>; Yuan, Perry <Perry.Yuan@amd.com>;
> Limonciello, Mario <Mario.Limonciello@amd.com>; Jinzhou Su
> <Jinzhou.Su@amd.com>; Meng, Li (Jassmine) <Li.Meng@amd.com>; linux-
> pm@vger.kernel.org; linux-kernel@vger.kernel.org
> Subject: [PATCH] cpufreq: amd-pstate: avoid uninitialized variable use
>
> From: Arnd Bergmann <arnd@arndb.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@arndb.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);
> }
>
> --
> 2.39.1

Thanks for your quick fix patch.

Reviewed-by: Yuan Perry <Perry.Yuan@amd.com>

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