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Commit d0981a1b authored by Thomas Gleixner's avatar Thomas Gleixner
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clocksource: Protect the watchdog rating changes with clocksource_mutex 



Martin pointed out that commit 6ea41d2529 (clocksource: Call
clocksource_change_rating() outside of watchdog_lock) has a
theoretical reference count problem. The calls to
clocksource_change_rating() are now done outside of the clocksource
mutex and outside of the watchdog lock. A concurrent
clocksource_unregister() could remove the clock.

Split out the code which changes the rating from
clocksource_change_rating() into __clocksource_change_rating().

Protect the clocksource_watchdog_work() code sequence with the
clocksource_mutex() and call __clocksource_change_rating().

LKML-Reference: <alpine.LFD.2.00.0908171038420.2782@localhost.localdomain>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
parent 6ea41d25

kernel/time/clocksource.c

+13 −5
Original line number Diff line number Diff line
@@ -131,6 +131,7 @@ static cycle_t watchdog_last; 
static int watchdog_running;



static void clocksource_watchdog_work(struct work_struct *work);

static void __clocksource_change_rating(struct clocksource *cs, int rating);



/*

 * Interval: 0.5sec Threshold: 0.0625s
@@ -309,6 +310,7 @@ static void clocksource_watchdog_work(struct work_struct *work) 
	unsigned long flags;

	LIST_HEAD(unstable);



	mutex_lock(&clocksource_mutex);

	spin_lock_irqsave(&watchdog_lock, flags);

	list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list)

		if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
@@ -322,8 +324,9 @@ static void clocksource_watchdog_work(struct work_struct *work) 
	/* Needs to be done outside of watchdog lock */

	list_for_each_entry_safe(cs, tmp, &unstable, wd_list) {

		list_del_init(&cs->wd_list);

		clocksource_change_rating(cs, 0);

		__clocksource_change_rating(cs, 0);

	}

	mutex_unlock(&clocksource_mutex);

}



#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
@@ -470,16 +473,21 @@ int clocksource_register(struct clocksource *cs) 
}

EXPORT_SYMBOL(clocksource_register);



static void __clocksource_change_rating(struct clocksource *cs, int rating)

{

	list_del(&cs->list);

	cs->rating = rating;

	clocksource_enqueue(cs);

	clocksource_select();

}



/**

 * clocksource_change_rating - Change the rating of a registered clocksource

 */

void clocksource_change_rating(struct clocksource *cs, int rating)

{

	mutex_lock(&clocksource_mutex);

	list_del(&cs->list);

	cs->rating = rating;

	clocksource_enqueue(cs);

	clocksource_select();

	__clocksource_change_rating(cs, rating);

	mutex_unlock(&clocksource_mutex);

}

EXPORT_SYMBOL(clocksource_change_rating);