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

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Message-Id: <20230207161256.271613-1-arnd@kernel.org>
Date:   Tue,  7 Feb 2023 17:12:51 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Huang Rui <ray.huang@....com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Wyes Karny <wyes.karny@....com>,
        Perry Yuan <Perry.Yuan@....com>,
        Mario Limonciello <Mario.Limonciello@....com>
Cc:     Arnd Bergmann <arnd@...db.de>, Perry Yuan <perry.yuan@....com>,
        Mario Limonciello <mario.limonciello@....com>,
        Jinzhou Su <Jinzhou.Su@....com>, Meng Li <li.meng@....com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] cpufreq: amd-pstate: avoid uninitialized variable use

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);
 }
 
-- 
2.39.1