Commit 5d33b883 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

clocksource: Always verify highres capability 



If a clocksource has a (wrong) high rating, but can't be used as a
timebase for oneshot tick mode, it is unconditionally selected even
when the system is already in oneshot tick mode. This causes full
system failure.

Verify the clocksource selection against the oneshot mode.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarJohn Stultz <john.stultz@linaro.org>
Cc: Magnus Damm <magnus.damm@gmail.com>
Link: http://lkml.kernel.org/r/20130425143435.635040849@linutronix.de


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent fc1f7d56

kernel/time/clocksource.c

+26 −5
Original line number Diff line number Diff line
@@ -553,6 +553,26 @@ static u64 clocksource_max_deferment(struct clocksource *cs) 


#ifndef CONFIG_ARCH_USES_GETTIMEOFFSET



static struct clocksource *clocksource_find_best(bool oneshot)

{

	struct clocksource *cs;



	if (!finished_booting || list_empty(&clocksource_list))

		return NULL;



	/*

	 * We pick the clocksource with the highest rating. If oneshot

	 * mode is active, we pick the highres valid clocksource with

	 * the best rating.

	 */

	list_for_each_entry(cs, &clocksource_list, list) {

		if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))

			continue;

		return cs;

	}

	return NULL;

}



/**

 * clocksource_select - Select the best clocksource available

 *
@@ -563,12 +583,14 @@ static u64 clocksource_max_deferment(struct clocksource *cs) 
 */

static void clocksource_select(void)

{

	bool oneshot = tick_oneshot_mode_active();

	struct clocksource *best, *cs;



	if (!finished_booting || list_empty(&clocksource_list))

	/* Find the best suitable clocksource */

	best = clocksource_find_best(oneshot);

	if (!best)

		return;

	/* First clocksource on the list has the best rating. */

	best = list_first_entry(&clocksource_list, struct clocksource, list);



	/* Check for the override clocksource. */

	list_for_each_entry(cs, &clocksource_list, list) {

		if (strcmp(cs->name, override_name) != 0)
@@ -578,8 +600,7 @@ static void clocksource_select(void) 
		 * capable clocksource if the tick code is in oneshot

		 * mode (highres or nohz)

		 */

		if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&

		    tick_oneshot_mode_active()) {

		if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {

			/* Override clocksource cannot be used. */

			printk(KERN_WARNING "Override clocksource %s is not "

			       "HRT compatible. Cannot switch while in "

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