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clocksource: sanity check sysfs clocksource changes

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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>
This commit is contained in:
john stultz 2009-01-21 22:53:22 -07:00 committed by Thomas Gleixner
parent 7d27558c41
commit 3f68535ada
3 changed files with 20 additions and 4 deletions
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2
include/linux/hrtimer.h
View File

@ -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);

4
kernel/hrtimer.c
View File

@ -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) { }

16
kernel/time/clocksource.c
View File

@ -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;
@ -537,6 +550,9 @@ sysfs_show_available_clocksources(struct sys_device *dev,
spin_lock_irq(&clocksource_lock);
list_for_each_entry(src, &clocksource_list, list) {
/* 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);