1 files changed, 8 insertions, 10 deletions

diff --git a/arch/x86/kernel/tsc_32.c b/arch/x86/kernel/tsc_32.c
index 068759db63dd..65b70637ad97 100644
--- a/arch/x86/kernel/tsc_32.c
+++ b/arch/x86/kernel/tsc_32.c
@@ -14,7 +14,10 @@
 
 #include "mach_timer.h"
 
-static int tsc_disabled;
+/* native_sched_clock() is called before tsc_init(), so
+   we must start with the TSC soft disabled to prevent
+   erroneous rdtsc usage on !cpu_has_tsc processors */
+static int tsc_disabled = -1;
 
 /*
  * On some systems the TSC frequency does not
@@ -402,25 +405,20 @@ void __init tsc_init(void)
 {
         int cpu;
 
-        if (!cpu_has_tsc || tsc_disabled) {
-                /* Disable the TSC in case of !cpu_has_tsc */
-                tsc_disabled = 1;
+        if (!cpu_has_tsc || tsc_disabled > 0)
                 return;
-        }
 
         cpu_khz = calculate_cpu_khz();
         tsc_khz = cpu_khz;
 
         if (!cpu_khz) {
                 mark_tsc_unstable("could not calculate TSC khz");
-                /*
-                 * We need to disable the TSC completely in this case
-                 * to prevent sched_clock() from using it.
-                 */
-                tsc_disabled = 1;
                 return;
         }
 
+        /* now allow native_sched_clock() to use rdtsc */
+        tsc_disabled = 0;
+
         printk("Detected %lu.%03lu MHz processor.\n",
                                 (unsigned long)cpu_khz / 1000,
                                 (unsigned long)cpu_khz % 1000);