clocksource: sanity check sysfs clocksource changes

Thomas, Andrew and Ingo pointed out that we don't have any safety checks
in the clocksource sysfs entries to make sure sysadmins don't try to
change the clocksource to a non high-res timer capable clocksource (such
as jiffies) when high-res timers (HRT) is enabled.  Doing so will likely
hang a system.

Correct this by filtering non HRT clocksources from available_clocksources
and not accepting non HRT clocksources with HRT enabled.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 0d2f7c8a33d6aa2983fd610bac1fb7b4ebc44cca..58021b0c396d477713ce42dec49bb3bce4701604 100644 (file)
--- 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 cb8a15c1958318c52c116d08e33003ad2ea0cc98..1a70c18cdffe5509efab2d9cd6cee9314789a2b4 100644 (file)
--- 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 80189f6f1c5a1f7a326c9490e18f571fc8f49ea7..18b9f5da4ee95a0887993b0ae1155ec6f44da01c 100644 (file)
--- 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);
        }