diff --git a/Documentation/lockstat.txt b/Documentation/lockstat.txt
index 9cb9138f7a79..65f4c795015d 100644
--- a/Documentation/lockstat.txt
+++ b/Documentation/lockstat.txt
@@ -62,8 +62,20 @@ applicable).
 It also tracks 4 contention points per class. A contention point is a call site
 that had to wait on lock acquisition.
 
+ - CONFIGURATION
+
+Lock statistics are enabled via CONFIG_LOCK_STATS.
+
  - USAGE
 
+Enable collection of statistics:
+
+# echo 1 >/proc/sys/kernel/lock_stat
+
+Disable collection of statistics:
+
+# echo 0 >/proc/sys/kernel/lock_stat
+
 Look at the current lock statistics:
 
 ( line numbers not part of actual output, done for clarity in the explanation
diff --git a/kernel/futex.c b/kernel/futex.c
index fb65e822fc41..d73ef1f3e55d 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -304,8 +304,14 @@ void put_futex_key(int fshared, union futex_key *key)
  */
 static int fault_in_user_writeable(u32 __user *uaddr)
 {
-	int ret = get_user_pages(current, current->mm, (unsigned long)uaddr,
-				 1, 1, 0, NULL, NULL);
+	struct mm_struct *mm = current->mm;
+	int ret;
+
+	down_read(&mm->mmap_sem);
+	ret = get_user_pages(current, mm, (unsigned long)uaddr,
+			     1, 1, 0, NULL, NULL);
+	up_read(&mm->mmap_sem);
+
 	return ret < 0 ? ret : 0;
 }
 
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index f5dcd36d3151..4f8df01dbe51 100644
--- a/kernel/lockdep.c
+++ b/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;
 }
@@ -379,7 +386,8 @@ static int save_trace(struct stack_trace *trace)
 	 * complete trace that maxes out the entries provided will be reported
 	 * as incomplete, friggin useless </rant>
 	 */
-	if (trace->entries[trace->nr_entries-1] == ULONG_MAX)
+	if (trace->nr_entries != 0 &&
+	    trace->entries[trace->nr_entries-1] == ULONG_MAX)
 		trace->nr_entries--;
 
 	trace->max_entries = trace->nr_entries;