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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>
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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

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) { }

18
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;
@ -537,7 +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);
}