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Commit 2aae7bcf authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Thomas Gleixner
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clocksource: Allow clocksource_mark_unstable() on unregistered clocksources 



Because of how the code flips between tsc-early and tsc clocksources
it might need to mark one or both unstable. The current code in
mark_tsc_unstable() only worked because previously it registered the
tsc clocksource once and then never touched it.

Since it now unregisters the tsc-early clocksource, it needs to know
if a clocksource got unregistered and the current cs->mult test
doesn't work for that. Instead use list_empty(&cs->list) to test for
registration.

Furthermore, since clocksource_mark_unstable() needs to place the cs
on the wd_list, it links the cs->list and cs->wd_list serialization.
It must not see a clocsource registered (!empty cs->list) but already
past dequeue_watchdog(). So place {en,de}queue{,_watchdog}() under the
same lock.

Provided cs->list is initialized to empty, this then allows us to
unconditionally use clocksource_mark_unstable(), regardless of the
registration state.

Fixes: aa83c457 ("x86/tsc: Introduce early tsc clocksource")
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: default avatarDiego Viola <diego.viola@gmail.com>
Cc: len.brown@intel.com
Cc: rjw@rjwysocki.net
Cc: diego.viola@gmail.com
Cc: rui.zhang@intel.com
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20180502135312.GS12217@hirez.programming.kicks-ass.net
parent e9088add

kernel/time/clocksource.c

+34 −16
Original line number Diff line number Diff line
@@ -119,6 +119,16 @@ static DEFINE_SPINLOCK(watchdog_lock); 
static int watchdog_running;

static atomic_t watchdog_reset_pending;



static void inline clocksource_watchdog_lock(unsigned long *flags)

{

	spin_lock_irqsave(&watchdog_lock, *flags);

}



static void inline clocksource_watchdog_unlock(unsigned long *flags)

{

	spin_unlock_irqrestore(&watchdog_lock, *flags);

}



static int clocksource_watchdog_kthread(void *data);

static void __clocksource_change_rating(struct clocksource *cs, int rating);
@@ -142,6 +152,9 @@ static void __clocksource_unstable(struct clocksource *cs) 
	cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);

	cs->flags |= CLOCK_SOURCE_UNSTABLE;



	if (list_empty(&cs->list))

		return;



	if (cs->mark_unstable)

		cs->mark_unstable(cs);
@@ -164,7 +177,7 @@ void clocksource_mark_unstable(struct clocksource *cs) 


	spin_lock_irqsave(&watchdog_lock, flags);

	if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {

		if (list_empty(&cs->wd_list))

		if (!list_empty(&cs->list) && list_empty(&cs->wd_list))

			list_add(&cs->wd_list, &watchdog_list);

		__clocksource_unstable(cs);

	}
@@ -319,9 +332,6 @@ static void clocksource_resume_watchdog(void) 


static void clocksource_enqueue_watchdog(struct clocksource *cs)

{

	unsigned long flags;



	spin_lock_irqsave(&watchdog_lock, flags);

	if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {

		/* cs is a clocksource to be watched. */

		list_add(&cs->wd_list, &watchdog_list);
@@ -331,7 +341,6 @@ static void clocksource_enqueue_watchdog(struct clocksource *cs) 
		if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)

			cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;

	}

	spin_unlock_irqrestore(&watchdog_lock, flags);

}



static void clocksource_select_watchdog(bool fallback)
@@ -373,9 +382,6 @@ static void clocksource_select_watchdog(bool fallback) 


static void clocksource_dequeue_watchdog(struct clocksource *cs)

{

	unsigned long flags;



	spin_lock_irqsave(&watchdog_lock, flags);

	if (cs != watchdog) {

		if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {

			/* cs is a watched clocksource. */
@@ -384,21 +390,19 @@ static void clocksource_dequeue_watchdog(struct clocksource *cs) 
			clocksource_stop_watchdog();

		}

	}

	spin_unlock_irqrestore(&watchdog_lock, flags);

}



static int __clocksource_watchdog_kthread(void)

{

	struct clocksource *cs, *tmp;

	unsigned long flags;

	LIST_HEAD(unstable);

	int select = 0;



	spin_lock_irqsave(&watchdog_lock, flags);

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

		if (cs->flags & CLOCK_SOURCE_UNSTABLE) {

			list_del_init(&cs->wd_list);

			list_add(&cs->wd_list, &unstable);

			__clocksource_change_rating(cs, 0);

			select = 1;

		}

		if (cs->flags & CLOCK_SOURCE_RESELECT) {
@@ -410,11 +414,6 @@ static int __clocksource_watchdog_kthread(void) 
	clocksource_stop_watchdog();

	spin_unlock_irqrestore(&watchdog_lock, flags);



	/* 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);

	}

	return select;

}
@@ -447,6 +446,9 @@ static inline int __clocksource_watchdog_kthread(void) { return 0; } 
static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }

void clocksource_mark_unstable(struct clocksource *cs) { }



static void inline clocksource_watchdog_lock(unsigned long *flags) { }

static void inline clocksource_watchdog_unlock(unsigned long *flags) { }



#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */



/**
@@ -779,14 +781,19 @@ EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale); 
 */

int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)

{

	unsigned long flags;



	/* Initialize mult/shift and max_idle_ns */

	__clocksource_update_freq_scale(cs, scale, freq);



	/* Add clocksource to the clocksource list */

	mutex_lock(&clocksource_mutex);



	clocksource_watchdog_lock(&flags);

	clocksource_enqueue(cs);

	clocksource_enqueue_watchdog(cs);

	clocksource_watchdog_unlock(&flags);



	clocksource_select();

	clocksource_select_watchdog(false);

	mutex_unlock(&clocksource_mutex);
@@ -808,8 +815,13 @@ static void __clocksource_change_rating(struct clocksource *cs, int rating) 
 */

void clocksource_change_rating(struct clocksource *cs, int rating)

{

	unsigned long flags;



	mutex_lock(&clocksource_mutex);

	clocksource_watchdog_lock(&flags);

	__clocksource_change_rating(cs, rating);

	clocksource_watchdog_unlock(&flags);



	clocksource_select();

	clocksource_select_watchdog(false);

	mutex_unlock(&clocksource_mutex);
@@ -821,6 +833,8 @@ EXPORT_SYMBOL(clocksource_change_rating); 
 */

static int clocksource_unbind(struct clocksource *cs)

{

	unsigned long flags;



	if (clocksource_is_watchdog(cs)) {

		/* Select and try to install a replacement watchdog. */

		clocksource_select_watchdog(true);
@@ -834,8 +848,12 @@ static int clocksource_unbind(struct clocksource *cs) 
		if (curr_clocksource == cs)

			return -EBUSY;

	}



	clocksource_watchdog_lock(&flags);

	clocksource_dequeue_watchdog(cs);

	list_del_init(&cs->list);

	clocksource_watchdog_unlock(&flags);



	return 0;

}