Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  lockdep: Avoid out of bounds array reference in save_trace()
  futex: Take mmap_sem for get_user_pages in fault_in_user_writeable
  lockstat: Add usage info to Documentation/lockstat.txt
  lockstat: Fix min, max times in /proc/lock_stats

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

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;
 }
 

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;