From 35d5d08a085c56f153458c3f5d8ce24123617faf Mon Sep 17 00:00:00 2001
From: Andrew Morton <akpm@linux-foundation.org>
Date: Wed, 14 Nov 2007 17:00:41 -0800
Subject: 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 arch/x86/lib/delay_32.c | 3 +++
 1 file changed, 3 insertions(+)

(limited to 'arch/x86/lib/delay_32.c')

diff --git a/arch/x86/lib/delay_32.c b/arch/x86/lib/delay_32.c
index 952e7a89c2ac..aad9d95469dc 100644
--- a/arch/x86/lib/delay_32.c
+++ b/arch/x86/lib/delay_32.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 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();
 }
 
 /*
-- 
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