linux-kernel - [tip:x86/urgent] x86: Remove indirect variable usage at arch/x86/kernel/tsc.c

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Message-ID: <tip-5a8aee6c809dc36e42b256566e5e28e244be3c74@git.kernel.org>
Date:	Wed, 17 Jun 2009 15:30:46 GMT
From:	tip-bot for Subrata Modak <subrata@...ux.vnet.ibm.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	andi@...stfloor.org, elendil@...net.nl, sachinp@...ux.vnet.ibm.com,
	subrata@...ux.vnet.ibm.com, balbir@...ux.vnet.ibm.com,
	tglx@...utronix.de, mingo@...e.hu
Subject: [tip:x86/urgent] x86: Remove indirect variable usage at arch/x86/kernel/tsc.c

Commit-ID:  5a8aee6c809dc36e42b256566e5e28e244be3c74
Gitweb:     http://git.kernel.org/tip/5a8aee6c809dc36e42b256566e5e28e244be3c74
Author:     Subrata Modak <subrata@...ux.vnet.ibm.com>
AuthorDate: Wed, 20 May 2009 11:51:15 +0530
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Wed, 17 Jun 2009 17:26:30 +0200

x86: Remove indirect variable usage at arch/x86/kernel/tsc.c

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 }

Also included fix expected by Frans Pop:

> No comments on your patch, but it might be good to also fix the incorrect
> indentation here: line 644 needs an extra tab.

Please refer:

  http://lkml.org/lkml/2009/5/19/312, and,
  http://lkml.org/lkml/2009/5/19/301.

Signed-off-by: Subrata Modak <subrata@...ux.vnet.ibm.com>
Cc: Sachin P Sant <sachinp@...ux.vnet.ibm.com>
Cc: Frans Pop <elendil@...net.nl>
Cc: Andi Kleen <andi@...stfloor.org>
Cc: Balbir Singh <balbir@...ux.vnet.ibm.com>
LKML-Reference: <20090520062115.23889.45487.sendpatchset@...ratamodak.linux.ibm.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>


---
 arch/x86/kernel/tsc.c |    7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 3e1c057..7714609 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -631,17 +631,16 @@ 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 = 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;
 #else
-	lpj = &boot_cpu_data.loops_per_jiffy;
+		lpj = &boot_cpu_data.loops_per_jiffy;
 #endif
 
 	if (!ref_freq) {
@@ -652,7 +651,7 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
 	if ((val == CPUFREQ_PRECHANGE  && freq->old < freq->new) ||
 			(val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
 			(val == CPUFREQ_RESUMECHANGE)) {
-		*lpj = 	cpufreq_scale(loops_per_jiffy_ref, ref_freq, freq->new);
+		*lpj = cpufreq_scale(loops_per_jiffy_ref, ref_freq, freq->new);
 
 		tsc_khz = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new);
 		if (!(freq->flags & CPUFREQ_CONST_LOOPS))
--
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