[patch 1/7] timers: Sanitize catchup_timer_jiffies() usage

[Thomas Gleixner <tglx@linutronix.de>]

[-- Attachment #1: timers-sanitize-catchup-jiffies.patch --]
[-- Type: text/plain, Size: 3247 bytes --]

catchup_timer_jiffies() has been applied blindly to several functions
without looking for possible better ways to do it.

1) internal_add_timer()

   Move the update to base->all_timers before we actually insert the
   timer into the wheel.

2) detach_if_pending()

   Again the update to base->all_timers allows us to explicitely do
   the timer_jiffies update in place, if this was the last timer which
   got removed.

3) __run_timers()

   We only check on entry, which is silly, because base->timer_jiffies
   can be behind - especially on NOHZ kernels - and if there is a
   single deferrable timer somewhere between base->timer_jiffies and
   jiffies we expire it and then loop until base->timer_jiffies ==
   jiffies.

   Move it into the loop.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/time/timer.c |   26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

Index: tip/kernel/time/timer.c
===================================================================
--- tip.orig/kernel/time/timer.c
+++ tip/kernel/time/timer.c
@@ -356,7 +356,7 @@ EXPORT_SYMBOL_GPL(set_timer_slack);
  * The caller must hold the tvec_base lock.  Returns true if the list
  * was empty and therefore ->timer_jiffies was updated.
  */
-static bool catchup_timer_jiffies(struct tvec_base *base)
+static inline bool catchup_timer_jiffies(struct tvec_base *base)
 {
 	if (!base->all_timers) {
 		base->timer_jiffies = jiffies;
@@ -411,7 +411,10 @@ __internal_add_timer(struct tvec_base *b
 
 static void internal_add_timer(struct tvec_base *base, struct timer_list *timer)
 {
-	(void)catchup_timer_jiffies(base);
+	/* Advance base->jiffies, if the base is empty */
+	if (!base->all_timers++)
+		base->timer_jiffies = jiffies;
+
 	__internal_add_timer(base, timer);
 	/*
 	 * Update base->active_timers and base->next_timer
@@ -421,7 +424,6 @@ static void internal_add_timer(struct tv
 		    time_before(timer->expires, base->next_timer))
 			base->next_timer = timer->expires;
 	}
-	base->all_timers++;
 
 	/*
 	 * Check whether the other CPU is in dynticks mode and needs
@@ -719,7 +721,6 @@ detach_expired_timer(struct timer_list *
 	if (!tbase_get_deferrable(timer->base))
 		base->active_timers--;
 	base->all_timers--;
-	(void)catchup_timer_jiffies(base);
 }
 
 static int detach_if_pending(struct timer_list *timer, struct tvec_base *base,
@@ -734,8 +735,9 @@ static int detach_if_pending(struct time
 		if (timer->expires == base->next_timer)
 			base->next_timer = base->timer_jiffies;
 	}
-	base->all_timers--;
-	(void)catchup_timer_jiffies(base);
+	/* If this was the last timer, advance base->jiffies */
+	if (!--base->all_timers)
+		base->timer_jiffies = jiffies;
 	return 1;
 }
 
@@ -1185,14 +1187,16 @@ static inline void __run_timers(struct t
 	struct timer_list *timer;
 
 	spin_lock_irq(&base->lock);
-	if (catchup_timer_jiffies(base)) {
-		spin_unlock_irq(&base->lock);
-		return;
-	}
+
 	while (time_after_eq(jiffies, base->timer_jiffies)) {
 		struct list_head work_list;
 		struct list_head *head = &work_list;
-		int index = base->timer_jiffies & TVR_MASK;
+		int index;
+
+		if (catchup_timer_jiffies(base))
+			break;
+
+		index = base->timer_jiffies & TVR_MASK;
 
 		/*
 		 * Cascade timers: