lockstat: Fix min, max times in /proc/lock_stats

Fix min, max times in /proc/lock_stats

(1) When collecting lock hold and wait times, if the current minimum
    time is zero, it will be replaced by the next time.

(2) When aggregating minimum and maximum lock hold and wait times
    accross cpus, the values are added, instead of selecting the
    minimum and maximum.

Signed-off-by: Frank Rowand <frank.rowand@am.sony.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <4B05BBAE.2050005@am.sony.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/lockdep.c

@@ -168,7 +168,7 @@ static void lock_time_inc(struct lock_time *lt, u64 time)
 	if (time > lt->max)
 		lt->max = time;
 
-	if (time < lt->min || !lt->min)
+	if (time < lt->min || !lt->nr)
 		lt->min = time;
 
 	lt->total += time;
@@ -177,8 +177,15 @@ static void lock_time_inc(struct lock_time *lt, u64 time)
 
 static inline void lock_time_add(struct lock_time *src, struct lock_time *dst)
 {
-	dst->min += src->min;
-	dst->max += src->max;
+	if (!src->nr)
+		return;
+
+	if (src->max > dst->max)
+		dst->max = src->max;
+
+	if (src->min < dst->min || !dst->nr)
+		dst->min = src->min;
+
 	dst->total += src->total;
 	dst->nr += src->nr;
 }