| From stable-bounces@linux.kernel.org Wed Nov 14 17:08:53 2007 |
| From: Andrew Morton <akpm@linux-foundation.org> |
| Date: Wed, 14 Nov 2007 17:00:41 -0800 |
| Subject: x86: disable preemption in delay_tsc() |
| To: torvalds@linux-foundation.org |
| Cc: mitov@issp.bas.bg, ak@suse.de, stable@kernel.org, tglx@linutronix.de, akpm@linux-foundation.org, mingo@elte.hu |
| Message-ID: <200711150100.lAF10fUR002915@imap1.linux-foundation.org> |
| |
| |
| 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); |
| |