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Subject[patch 10/29] x86: disable preemption in delay_tsc()

2.6.23-stable review patch. If anyone has any objections, please let us
know.

------------------
From: Andrew Morton <akpm@linux-foundation.org>

patch 35d5d08a085c56f153458c3f5d8ce24123617faf in mainline.

Marin Mitov points out that delay_tsc() can misbehave if it is preempted and
rescheduled on a different CPU which has a skewed TSC. Fix it by disabling
preemption.

(I assume that the worst-case behaviour here is a stall of 2^32 cycles)

Cc: Andi Kleen <ak@suse.de>
Cc: Marin Mitov <mitov@issp.bas.bg>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/i386/lib/delay.c | 3 +++
arch/x86_64/lib/delay.c | 11 +++++++----
2 files changed, 10 insertions(+), 4 deletions(-)

--- a/arch/i386/lib/delay.c
+++ b/arch/i386/lib/delay.c
@@ -12,6 +12,7 @@

#include <linux/module.h>
#include <linux/sched.h>
+#include <linux/preempt.h>
#include <linux/delay.h>

#include <asm/processor.h>
@@ -42,11 +43,13 @@ static void delay_tsc(unsigned long loop
{
unsigned long bclock, now;

+ preempt_disable(); /* TSC's are per-cpu */
rdtscl(bclock);
do {
rep_nop();
rdtscl(now);
} while ((now-bclock) < loops);
+ preempt_enable();
}

/*
--- a/arch/x86_64/lib/delay.c
+++ b/arch/x86_64/lib/delay.c
@@ -10,7 +10,9 @@

#include <linux/module.h>
#include <linux/sched.h>
+#include <linux/preempt.h>
#include <linux/delay.h>
+
#include <asm/delay.h>
#include <asm/msr.h>

@@ -27,14 +29,15 @@ int read_current_timer(unsigned long *ti
void __delay(unsigned long loops)
{
unsigned bclock, now;
-
+
+ preempt_disable(); /* TSC's are pre-cpu */
rdtscl(bclock);
- do
- {
+ do {
rep_nop();
rdtscl(now);
}
- while((now-bclock) < loops);
+ while ((now-bclock) < loops);
+ preempt_enable();
}
EXPORT_SYMBOL(__delay);

--
-
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