time: Kill xtime_lock, replacing it with jiffies_lock

Now that timekeeping is protected by its own locks, rename
the xtime_lock to jifffies_lock to better describe what it
protects.

CC: Thomas Gleixner <tglx@linutronix.de>
CC: Eric Dumazet <eric.dumazet@gmail.com>
CC: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>

drivers/clocksource/i8253.c

@@ -35,7 +35,7 @@ static cycle_t i8253_read(struct clocksource *cs)
 
 	raw_spin_lock_irqsave(&i8253_lock, flags);
 	/*
-	 * Although our caller may have the read side of xtime_lock,
+	 * Although our caller may have the read side of jiffies_lock,
 	 * this is now a seqlock, and we are cheating in this routine
 	 * by having side effects on state that we cannot undo if
 	 * there is a collision on the seqlock and our caller has to

include/linux/jiffies.h

@@ -70,11 +70,12 @@ extern int register_refined_jiffies(long clock_tick_rate);
 
 /*
  * The 64-bit value is not atomic - you MUST NOT read it
- * without sampling the sequence number in xtime_lock.
+ * without sampling the sequence number in jiffies_lock.
  * get_jiffies_64() will do this for you as appropriate.
  */
 extern u64 __jiffy_data jiffies_64;
 extern unsigned long volatile __jiffy_data jiffies;
+extern seqlock_t jiffies_lock;
 
 #if (BITS_PER_LONG < 64)
 u64 get_jiffies_64(void);

kernel/time/jiffies.c

@@ -67,6 +67,8 @@ static struct clocksource clocksource_jiffies = {
 	.shift		= JIFFIES_SHIFT,
 };
 
+__cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock);
+
 #if (BITS_PER_LONG < 64)
 u64 get_jiffies_64(void)
 {
@@ -74,9 +76,9 @@ u64 get_jiffies_64(void)
 	u64 ret;
 
 	do {
-		seq = read_seqbegin(&xtime_lock);
+		seq = read_seqbegin(&jiffies_lock);
 		ret = jiffies_64;
-	} while (read_seqretry(&xtime_lock, seq));
+	} while (read_seqretry(&jiffies_lock, seq));
 	return ret;
 }
 EXPORT_SYMBOL(get_jiffies_64);

kernel/time/tick-common.c

@@ -63,13 +63,13 @@ int tick_is_oneshot_available(void)
 static void tick_periodic(int cpu)
 {
 	if (tick_do_timer_cpu == cpu) {
-		write_seqlock(&xtime_lock);
+		write_seqlock(&jiffies_lock);
 
 		/* Keep track of the next tick event */
 		tick_next_period = ktime_add(tick_next_period, tick_period);
 
 		do_timer(1);
-		write_sequnlock(&xtime_lock);
+		write_sequnlock(&jiffies_lock);
 	}
 
 	update_process_times(user_mode(get_irq_regs()));
@@ -130,9 +130,9 @@ void tick_setup_periodic(struct clock_event_device *dev, int broadcast)
 		ktime_t next;
 
 		do {
-			seq = read_seqbegin(&xtime_lock);
+			seq = read_seqbegin(&jiffies_lock);
 			next = tick_next_period;
-		} while (read_seqretry(&xtime_lock, seq));
+		} while (read_seqretry(&jiffies_lock, seq));
 
 		clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
 

kernel/time/tick-internal.h

@@ -141,4 +141,3 @@ static inline int tick_device_is_functional(struct clock_event_device *dev)
 #endif
 
 extern void do_timer(unsigned long ticks);
-extern seqlock_t xtime_lock;

kernel/time/tick-sched.c

@@ -31,7 +31,7 @@
 static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
 
 /*
- * The time, when the last jiffy update happened. Protected by xtime_lock.
+ * The time, when the last jiffy update happened. Protected by jiffies_lock.
  */
 static ktime_t last_jiffies_update;
 
@@ -49,14 +49,14 @@ static void tick_do_update_jiffies64(ktime_t now)
 	ktime_t delta;
 
 	/*
-	 * Do a quick check without holding xtime_lock:
+	 * Do a quick check without holding jiffies_lock:
 	 */
 	delta = ktime_sub(now, last_jiffies_update);
 	if (delta.tv64 < tick_period.tv64)
 		return;
 
-	/* Reevalute with xtime_lock held */
+	/* Reevalute with jiffies_lock held */
-	write_seqlock(&xtime_lock);
+	write_seqlock(&jiffies_lock);
 
 	delta = ktime_sub(now, last_jiffies_update);
 	if (delta.tv64 >= tick_period.tv64) {
@@ -79,7 +79,7 @@ static void tick_do_update_jiffies64(ktime_t now)
 		/* Keep the tick_next_period variable up to date */
 		tick_next_period = ktime_add(last_jiffies_update, tick_period);
 	}
-	write_sequnlock(&xtime_lock);
+	write_sequnlock(&jiffies_lock);
 }
 
 /*
@@ -89,12 +89,12 @@ static ktime_t tick_init_jiffy_update(void)
 {
 	ktime_t period;
 
-	write_seqlock(&xtime_lock);
+	write_seqlock(&jiffies_lock);
 	/* Did we start the jiffies update yet ? */
 	if (last_jiffies_update.tv64 == 0)
 		last_jiffies_update = tick_next_period;
 	period = last_jiffies_update;
-	write_sequnlock(&xtime_lock);
+	write_sequnlock(&jiffies_lock);
 	return period;
 }
 
@@ -282,11 +282,11 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
 
 	/* Read jiffies and the time when jiffies were updated last */
 	do {
-		seq = read_seqbegin(&xtime_lock);
+		seq = read_seqbegin(&jiffies_lock);
 		last_update = last_jiffies_update;
 		last_jiffies = jiffies;
 		time_delta = timekeeping_max_deferment();
-	} while (read_seqretry(&xtime_lock, seq));
+	} while (read_seqretry(&jiffies_lock, seq));
 
 	if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) || printk_needs_cpu(cpu) ||
 	    arch_needs_cpu(cpu)) {
@@ -658,7 +658,7 @@ static void tick_nohz_handler(struct clock_event_device *dev)
 	 * concurrency: This happens only when the cpu in charge went
 	 * into a long sleep. If two cpus happen to assign themself to
 	 * this duty, then the jiffies update is still serialized by
-	 * xtime_lock.
+	 * jiffies_lock.
 	 */
 	if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
 		tick_do_timer_cpu = cpu;
@@ -810,7 +810,7 @@ static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
 	 * concurrency: This happens only when the cpu in charge went
 	 * into a long sleep. If two cpus happen to assign themself to
 	 * this duty, then the jiffies update is still serialized by
-	 * xtime_lock.
+	 * jiffies_lock.
 	 */
 	if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
 		tick_do_timer_cpu = cpu;

kernel/time/timekeeping.c

@@ -25,12 +25,6 @@
 
 static struct timekeeper timekeeper;
 
-/*
- * This read-write spinlock protects us from races in SMP while
- * playing with xtime.
- */
-__cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock);
-
 /* flag for if timekeeping is suspended */
 int __read_mostly timekeeping_suspended;
 
@@ -1299,9 +1293,7 @@ struct timespec get_monotonic_coarse(void)
 }
 
 /*
- * The 64-bit jiffies value is not atomic - you MUST NOT read it
+ * Must hold jiffies_lock
- * without sampling the sequence number in xtime_lock.
- * jiffies is defined in the linker script...
  */
 void do_timer(unsigned long ticks)
 {
@@ -1389,7 +1381,7 @@ EXPORT_SYMBOL_GPL(ktime_get_monotonic_offset);
  */
 void xtime_update(unsigned long ticks)
 {
-	write_seqlock(&xtime_lock);
+	write_seqlock(&jiffies_lock);
 	do_timer(ticks);
-	write_sequnlock(&xtime_lock);
+	write_sequnlock(&jiffies_lock);
 }