rcutorture: Move to dynamic initialization of rcu_fwds

In order to add multiple call_rcu() forward-progress kthreads, it will
be necessary to dynamically allocate and initialize.  This commit
therefore moves the initialization from compile time to instead
immediately precede thread-creation time.

Signed-off-by: Paul E. McKenney <[email protected]>

Author: paulmckrcu

kernel/rcu/rcutorture.c

@@ -1686,11 +1686,7 @@ struct rcu_fwd {
 	unsigned long rcu_launder_gp_seq_start;
 };
 
-struct rcu_fwd rcu_fwds = {
-	.rcu_fwd_lock = __SPIN_LOCK_UNLOCKED(rcu_fwds.rcu_fwd_lock),
-	.rcu_fwd_cb_tail = &rcu_fwds.rcu_fwd_cb_head,
-};
-
+struct rcu_fwd rcu_fwds;
 bool rcu_fwd_emergency_stop;
 
 static void rcu_torture_fwd_cb_hist(struct rcu_fwd *rfp)
@@ -2026,6 +2022,8 @@ static int __init rcu_torture_fwd_prog_init(void)
 		WARN_ON(1); /* Make sure rcutorture notices conflict. */
 		return 0;
 	}
+	spin_lock_init(&rcu_fwds.rcu_fwd_lock);
+	rcu_fwds.rcu_fwd_cb_tail = &rcu_fwds.rcu_fwd_cb_head;
 	if (fwd_progress_holdoff <= 0)
 		fwd_progress_holdoff = 1;
 	if (fwd_progress_div <= 0)