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    SubjectRe: [PATCH] Remove indirect variable usage at arch/x86/kernel/tsc.c
    Hi!

    > CC arch/x86/kernel/tsc.o
    > 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
    >
    > However, there seems to be no practical usage of variable 'dummy'
    > in the following piece of code:
    >
    > 630 static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
    > 631 void *data)
    > 632 {
    > 633 struct cpufreq_freqs *freq = data;
    > 634 unsigned long *lpj, dummy;
    > 635
    > 636 if (cpu_has(&cpu_data(freq->cpu), X86_FEATURE_CONSTANT_TSC))
    > 637 return 0;
    > 638
    > 639 lpj = &dummy;
    > 640 if (!(freq->flags & CPUFREQ_CONST_LOOPS))
    > 641 #ifdef CONFIG_SMP
    > 642 lpj = &cpu_data(freq->cpu).loops_per_jiffy;
    > 643 #else
    > 644 lpj = &boot_cpu_data.loops_per_jiffy;
    > 645 #endif
    > 646
    >
    > 'lpj' probably will get to point to some address after this if() statement.
    >
    > 647 if (!ref_freq) {
    > 648 ref_freq = freq->old;
    > 649 loops_per_jiffy_ref = *lpj;
    >
    > And, if it does, then "loops_per_jiffy_ref" will have a proper value,
    > else, even with "lpj = &dummy" will not gurantee "loops_per_jiffy_ref = *lpj"
    > to have the expected value.

    But that's a bug to be fixed, I'd say? ... actually I believe you are
    introducing a bug here. Yes, old code would put random numbers in
    loops_per_jiffy_ref for !CPUFREQ_CONST_LOOPS, but you are introducing
    oops there.

    Have you tested the code?

    > @@ -631,12 +631,11 @@ static int time_cpufreq_notifier(struct
    > void *data)
    > {
    > struct cpufreq_freqs *freq = data;
    > - unsigned long *lpj, dummy;
    > + unsigned long *lpj = NULL;
    >
    > if (cpu_has(&cpu_data(freq->cpu), X86_FEATURE_CONSTANT_TSC))
    > return 0;
    >
    > - lpj = &dummy;
    > if (!(freq->flags & CPUFREQ_CONST_LOOPS))
    > #ifdef CONFIG_SMP
    > lpj = &cpu_data(freq->cpu).loops_per_jiffy;
    >

    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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