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>

diff --git a/arch/x86/lib/delay_32.c b/arch/x86/lib/delay_32.c
index 952e7a8..aad9d95 100644 (file)
--- 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();
 }
 
 /*

diff --git a/arch/x86/lib/delay_64.c b/arch/x86/lib/delay_64.c
index 0ebbfb9..45cdd3f 100644 (file)
--- a/arch/x86/lib/delay_64.c
+++ b/arch/x86/lib/delay_64.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 *timer_value)
 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);