timers: Track total number of timers in list

upstream commit: fff421580f512fc044cc7421fdff31a7a6997350

Currently, the tvec_base structure's ->active_timers field tracks only
the non-deferrable timers, which means that even if ->active_timers is
zero, there might well be deferrable timers in the list.  This commit
therefore adds an ->all_timers field to track all the timers, whether
deferrable or not.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Mike Galbraith <bitbucket@online.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/timer.c b/kernel/timer.c
index 8f1687a..251fdac 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -84,6 +84,7 @@
 	unsigned long timer_jiffies;
 	unsigned long next_timer;
 	unsigned long active_timers;
+	unsigned long all_timers;
 	struct tvec_root tv1;
 	struct tvec tv2;
 	struct tvec tv3;
@@ -395,6 +396,7 @@
 			base->next_timer = timer->expires;
 		base->active_timers++;
 	}
+	base->all_timers++;
 }
 
 #ifdef CONFIG_TIMER_STATS
@@ -674,6 +676,7 @@
 	detach_timer(timer, true);
 	if (!tbase_get_deferrable(timer->base))
 		base->active_timers--;
+	base->all_timers--;
 }
 
 static int detach_if_pending(struct timer_list *timer, struct tvec_base *base,
@@ -688,6 +691,7 @@
 		if (timer->expires == base->next_timer)
 			base->next_timer = base->timer_jiffies;
 	}
+	base->all_timers--;
 	return 1;
 }
 
@@ -1677,6 +1681,7 @@
 	base->timer_jiffies = jiffies;
 	base->next_timer = base->timer_jiffies;
 	base->active_timers = 0;
+	base->all_timers = 0;
 	return 0;
 }