3 files changed, 20 insertions, 4 deletions

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 0d2f7c8a33d6..58021b0c396d 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -305,7 +305,7 @@ static inline int hrtimer_is_hres_active(struct hrtimer *timer)
 
 extern ktime_t ktime_get(void);
 extern ktime_t ktime_get_real(void);
-
+extern int hrtimer_hres_active(void);
 
 DECLARE_PER_CPU(struct tick_device, tick_cpu_device);
 
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index cb8a15c19583..1a70c18cdffe 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -476,7 +476,7 @@ static inline int hrtimer_is_hres_enabled(void)
 /*
  * Is the high resolution mode active ?
  */
-static inline int hrtimer_hres_active(void)
+int hrtimer_hres_active(void)
 {
         return __get_cpu_var(hrtimer_bases).hres_active;
 }
@@ -704,7 +704,7 @@ static int hrtimer_switch_to_hres(void)
 
 #else
 
-static inline int hrtimer_hres_active(void) { return 0; }
+int hrtimer_hres_active(void) { return 0; }
 static inline int hrtimer_is_hres_enabled(void) { return 0; }
 static inline int hrtimer_switch_to_hres(void) { return 0; }
 static inline void hrtimer_force_reprogram(struct hrtimer_cpu_base *base) { }
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 80189f6f1c5a..18b9f5da4ee9 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -30,6 +30,7 @@
 #include <linux/module.h>
 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
 #include <linux/tick.h>
+#include <linux/hrtimer.h>
 
 void timecounter_init(struct timecounter *tc,
                       const struct cyclecounter *cc,
@@ -509,6 +510,18 @@ static ssize_t sysfs_override_clocksource(struct sys_device *dev,
                 }
         }
 
+        /*
+         * Check to make sure we don't switch to a non-HRT usable
+         * clocksource if HRT is enabled and running
+         */
+        if (hrtimer_hres_active() &&
+            !(ovr->flags & CLOCK_SOURCE_VALID_FOR_HRES)) {
+                printk(KERN_WARNING "%s clocksource is not HRT compatible. "
+                        "Cannot switch while in HRT mode\n", ovr->name);
+                ovr = NULL;
+                override_name[0] = 0;
+        }
+
         /* Reselect, when the override name has changed */
         if (ovr != clocksource_override) {
                 clocksource_override = ovr;
@@ -537,7 +550,10 @@ sysfs_show_available_clocksources(struct sys_device *dev,
 
         spin_lock_irq(&clocksource_lock);
         list_for_each_entry(src, &clocksource_list, list) {
-                count += snprintf(buf + count,
+                /* Don't show non-HRES clocksource if HRES is enabled */
+                if (!hrtimer_hres_active() ||
+                                (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
+                        count += snprintf(buf + count,
                                   max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
                                   "%s ", src->name);
         }