timers: Remove must_forward_clk

There is no reason to keep this guard around. The code makes sure that
base->clk remains sane and won't be forwarded beyond jiffies nor set
backward.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200717140551.29076-12-frederic@kernel.org

kernel/time/timer.c

@@ -205,7 +205,6 @@ struct timer_base {
 	unsigned long		next_expiry;
 	unsigned int		cpu;
 	bool			is_idle;
-	bool			must_forward_clk;
 	DECLARE_BITMAP(pending_map, WHEEL_SIZE);
 	struct hlist_head	vectors[WHEEL_SIZE];
 } ____cacheline_aligned;
@@ -888,12 +887,13 @@ get_target_base(struct timer_base *base, unsigned tflags)
 
 static inline void forward_timer_base(struct timer_base *base)
 {
-	unsigned long jnow;
+	unsigned long jnow = READ_ONCE(jiffies);
 
-	if (!base->must_forward_clk)
-		return;
-
-	jnow = READ_ONCE(jiffies);
+	/*
+	 * No need to forward if we are close enough below jiffies.
+	 * Also while executing timers, base->clk is 1 offset ahead
+	 * of jiffies to avoid endless requeuing to current jffies.
+	 */
 	if ((long)(jnow - base->clk) < 2)
 		return;
 
@@ -1722,24 +1722,15 @@ static inline void __run_timers(struct timer_base *base)
 	timer_base_lock_expiry(base);
 	raw_spin_lock_irq(&base->lock);
 
-	/*
-	 * timer_base::must_forward_clk must be cleared before running
-	 * timers so that any timer functions that call mod_timer() will
-	 * not try to forward the base.
-	 */
-	base->must_forward_clk = false;
-
 	while (time_after_eq(jiffies, base->clk) &&
 	       time_after_eq(jiffies, base->next_expiry)) {
-
 		levels = collect_expired_timers(base, heads);
 		base->clk++;
 		base->next_expiry = __next_timer_interrupt(base);
 
 		while (levels--)
 			expire_timers(base, heads + levels);
 	}
-	base->must_forward_clk = true;
 	raw_spin_unlock_irq(&base->lock);
 	timer_base_unlock_expiry(base);
 }
@@ -1935,7 +1926,6 @@ int timers_prepare_cpu(unsigned int cpu)
 		base->clk = jiffies;
 		base->next_expiry = base->clk + NEXT_TIMER_MAX_DELTA;
 		base->is_idle = false;
-		base->must_forward_clk = true;
 	}
 	return 0;
 }