locktorture: Use private random-number generators

Both lock_torture_writer() and lock_torture_reader() use the "static"
keyword on their DEFINE_TORTURE_RANDOM(rand) declarations, which means
that a single instance of a random-number generator are shared among all
the writers and another is shared among all the readers.  Unfortunately,
this random-number generator was not designed for concurrent access.
This commit therefore removes both "static" keywords so that each reader
and each writer gets its own random-number generator.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/locking/locktorture.c

@@ -618,7 +618,7 @@ static struct lock_torture_ops percpu_rwsem_lock_ops = {
 static int lock_torture_writer(void *arg)
 {
 	struct lock_stress_stats *lwsp = arg;
-	static DEFINE_TORTURE_RANDOM(rand);
+	DEFINE_TORTURE_RANDOM(rand);
 
 	VERBOSE_TOROUT_STRING("lock_torture_writer task started");
 	set_user_nice(current, MAX_NICE);
@@ -655,7 +655,7 @@ static int lock_torture_writer(void *arg)
 static int lock_torture_reader(void *arg)
 {
 	struct lock_stress_stats *lrsp = arg;
-	static DEFINE_TORTURE_RANDOM(rand);
+	DEFINE_TORTURE_RANDOM(rand);
 
 	VERBOSE_TOROUT_STRING("lock_torture_reader task started");
 	set_user_nice(current, MAX_NICE);