Commit 3f68535a authored by john stultz's avatar john stultz Committed by Thomas Gleixner
Browse files

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: default avatarJohn Stultz <johnstul@us.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 7d27558c

include/linux/hrtimer.h

+1 −1
Original line number Diff line number Diff line
@@ -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);

kernel/hrtimer.c

+2 −2
Original line number Diff line number Diff line
@@ -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) { }

kernel/time/clocksource.c

+17 −1
Original line number Diff line number Diff line
@@ -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);

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