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

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Date:   Thu, 9 Feb 2023 20:22:55 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Huang Rui <ray.huang@....com>, Arnd Bergmann <arnd@...nel.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Karny, Wyes" <Wyes.Karny@....com>,
        "Yuan, Perry" <Perry.Yuan@....com>,
        "Limonciello, Mario" <Mario.Limonciello@....com>,
        Arnd Bergmann <arnd@...db.de>, Jinzhou Su <Jinzhou.Su@....com>,
        "Meng, Li (Jassmine)" <Li.Meng@....com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: amd-pstate: avoid uninitialized variable use

On Thu, Feb 9, 2023 at 6:04 AM Huang Rui <ray.huang@....com> wrote:
>
> On Wed, Feb 08, 2023 at 12:12:51AM +0800, 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>
>
> Thanks!
>
> Acked-by: Huang Rui <ray.huang@....com>
>
> > ---
> >  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);
> >  }
> >
> > --

Applied, thanks!