Recent hrtimer code will set the start info to a hrtimer only when that

flag is set, then the start info of all hrtimers will always be
uninitialised before a "echo 1 > /proc/timer_stats", thus the
/proc/timer_lists will have something like:

active timers:
 #0: <c27d46b0>, tick_sched_timer, S:01, <(null)>, /-1
 # expires at 91062000000-91062000000 nsecs [in 156071 to 156071 nsecs]
 #1: <efb81b6c>, hrtimer_wakeup, S:01, <(null)>, /-1
 # expires at 91062300331-91062350331 nsecs [in 456402 to 506402 nsecs]
 #2: <efac9b6c>, hrtimer_wakeup, S:01, <(null)>, /-1
 # expires at 91068699811-91068749811 nsecs [in 6855882 to 6905882 nsecs]
 #3: <efacdb6c>, hrtimer_wakeup, S:01, <(null)>, /-1
 # expires at 91068755511-91068805511 nsecs [in 6911582 to 6961582 nsecs]
 #4: <efa95b6c>, hrtimer_wakeup, S:01, <(null)>, /-1
 # expires at 91068806066-91068856066 nsecs [in 6962137 to 7012137 nsecs]
 .....

This patch fixes it.
Signed-off-by: Feng Tang <feng.tang@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/hrtimer.h

@@ -457,8 +457,6 @@ extern void __timer_stats_hrtimer_set_start_info(struct hrtimer *timer,
 
 static inline void timer_stats_hrtimer_set_start_info(struct hrtimer *timer)
 {
-	if (likely(!timer_stats_active))
-		return;
 	__timer_stats_hrtimer_set_start_info(timer, __builtin_return_address(0));
 }
 

kernel/hrtimer.c

@@ -750,7 +750,7 @@ static inline void hrtimer_init_timer_hres(struct hrtimer *timer) { }
 #ifdef CONFIG_TIMER_STATS
 void __timer_stats_hrtimer_set_start_info(struct hrtimer *timer, void *addr)
 {
-	if (timer->start_site)
+	if (timer->start_site == addr && timer->start_pid == current->pid)
 		return;
 
 	timer->start_site = addr;