Messages in this thread Patch in this message | | | From | Subrata Modak <> | Date | Tue, 19 May 2009 23:33:07 +0530 | Subject | [PATCH] Remove indirect variable usage at arch/x86/kernel/tsc.c |
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Hi,
The following warning is generated on compilation:
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.
650 tsc_khz_ref = tsc_khz; 651 } 652 if ((val == CPUFREQ_PRECHANGE && freq->old < freq->new) || 653 (val == CPUFREQ_POSTCHANGE && freq->old > freq->new) || 654 (val == CPUFREQ_RESUMECHANGE)) { 655 *lpj = cpufreq_scale(loops_per_jiffy_ref, ref_freq, freq->new); 656 657 tsc_khz = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new); 658 if (!(freq->flags & CPUFREQ_CONST_LOOPS)) 659 mark_tsc_unstable("cpufreq changes"); 660 } 661 662 set_cyc2ns_scale(tsc_khz, freq->cpu); 663 664 return 0; 665 }
Is there any specific reason for 'dummy' to exist in this function ? If not, i would like to propose the following fix.
Signed-off-by: Subrata Modak <subrata@linux.vnet.ibm.com> To: <x86@kernel.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Balbir Singh <balbir@linux.vnet.ibm.com> Cc: Sachin P Sant <sachinp@linux.vnet.ibm.com> Cc: Linux Kernel <linux-kernel@vger.kernel.org> Cc: Andi Kleen <andi@firstfloor.org> Subject: [PATCH] Remove indirect variable usage at arch/x86/kernel/tsc.c ---
--- a/arch/x86/kernel/tsc.c 2009-05-19 00:57:26.000000000 +0530 +++ b/arch/x86/kernel/tsc.c 2009-05-19 21:45:46.000000000 +0530 @@ -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; --- Regards-- Subrata
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