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Commit 35d5d08a authored by Andrew Morton's avatar Andrew Morton Committed by Linus Torvalds
Browse files

x86: disable preemption in delay_tsc() 



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>
Cc: <stable@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7eea4364

arch/x86/lib/delay_32.c

+3 −0
Original line number Diff line number Diff line
@@ -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 loops) 
{

	unsigned long bclock, now;



	preempt_disable();		/* TSC's are per-cpu */

	rdtscl(bclock);

	do {

		rep_nop();

		rdtscl(now);

	} while ((now-bclock) < loops);

	preempt_enable();

}



/*

arch/x86/lib/delay_64.c

+7 −4
Original line number Diff line number Diff line
@@ -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>
@@ -28,13 +30,14 @@ 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);

	preempt_enable();

}

EXPORT_SYMBOL(__delay);