Messages in this thread Patch in this message |  | | | Date | Mon, 1 Jun 2009 12:29:55 -0400 | | From | Dave Jones <> | | Subject | Re: fishy code in arch/x86/kernel/tsc.c:time_cpufreq_notifier() |
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On Mon, Jun 01, 2009 at 10:21:04AM -0400, Christoph Hellwig wrote: > Just notice the following error from gcc 4.4: > > arch/x86/kernel/tsc.c: In function 'time_cpufreq_notifier': > arch/x86/kernel/tsc.c:634: warning: 'dummy' may be used uninitialized in this function > > where we do have CONFIG_SMP set, freq->flags & CPUFREQ_CONST_LOOPS is > true and ref_freq is false. > > Can that case actually happen?
I think you're right, though the circumstances for hitting it are really low. Nearly all SMP capable cpufreq drivers set CPUFREQ_CONST_LOOPS. powernow-k8 is really the only exception. The older CPUs were typically only ever UP. (powernow-k7 never supported SMP for eg)
It's probably worth fixing.
I think the patch below is closer to the actual intent, with the bonus of being a lot more readable.
Sanity check?
Dave
Fix possible uninitialized use of dummy, by just removing it, and making the setting of lpj more obvious.
Signed-off-by: Dave Jones <davej@redhat.com>
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index d57de05..78c54ea 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -631,17 +631,15 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data) { struct cpufreq_freqs *freq = data; - unsigned long *lpj, dummy; + unsigned long *lpj; if (cpu_has(&cpu_data(freq->cpu), X86_FEATURE_CONSTANT_TSC)) return 0; - lpj = &dummy; - if (!(freq->flags & CPUFREQ_CONST_LOOPS)) + lpj = &boot_cpu_data.loops_per_jiffy; #ifdef CONFIG_SMP + if (!(freq->flags & CPUFREQ_CONST_LOOPS)) lpj = &cpu_data(freq->cpu).loops_per_jiffy; -#else - lpj = &boot_cpu_data.loops_per_jiffy; #endif if (!ref_freq) {
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