[PATCH] rcu_torture_lock deadlock fix

rcu_torture_lock is used in a softirq-unsafe manner, but it is also
taken by rcu_torture_cb(), which may execute in softirq-context,
resulting in potential deadlocks.

The fix is to acquire rcu_torture_lock in a softirq-safe manner.  With
this fix applied, the rcu-torture code passes validation.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Paul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/rcutorture.c

@@ -114,16 +114,16 @@ rcu_torture_alloc(void)
 {
 	struct list_head *p;
 
-	spin_lock(&rcu_torture_lock);
+	spin_lock_bh(&rcu_torture_lock);
 	if (list_empty(&rcu_torture_freelist)) {
 		atomic_inc(&n_rcu_torture_alloc_fail);
-		spin_unlock(&rcu_torture_lock);
+		spin_unlock_bh(&rcu_torture_lock);
 		return NULL;
 	}
 	atomic_inc(&n_rcu_torture_alloc);
 	p = rcu_torture_freelist.next;
 	list_del_init(p);
-	spin_unlock(&rcu_torture_lock);
+	spin_unlock_bh(&rcu_torture_lock);
 	return container_of(p, struct rcu_torture, rtort_free);
 }
 
@@ -134,9 +134,9 @@ static void
 rcu_torture_free(struct rcu_torture *p)
 {
 	atomic_inc(&n_rcu_torture_free);
-	spin_lock(&rcu_torture_lock);
+	spin_lock_bh(&rcu_torture_lock);
 	list_add_tail(&p->rtort_free, &rcu_torture_freelist);
-	spin_unlock(&rcu_torture_lock);
+	spin_unlock_bh(&rcu_torture_lock);
 }
 
 static void