rcu: Make rcu_report_unblock_qs_rnp() warn on violated preconditions

If rcu_report_unblock_qs_rnp() is invoked on something other than
preemptible RCU or if there are still preempted tasks blocking the
current grace period, something went badly wrong in the caller.
This commit therefore adds WARN_ON_ONCE() to these conditions, but
leaving the legitimate reason for early exit (rnp->qsmask != 0)
unwarned.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 3fe854a15d8282d5544149ba9d8d8ad996cba466..85417584ffd08607f11a257c17d7f22761df1673 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2308,8 +2308,10 @@ static void rcu_report_unblock_qs_rnp(struct rcu_state *rsp,
        struct rcu_node *rnp_p;
 
        raw_lockdep_assert_held_rcu_node(rnp);
-       if (rcu_state_p == &rcu_sched_state || rsp != rcu_state_p ||
-           rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
+       if (WARN_ON_ONCE(rcu_state_p == &rcu_sched_state) ||
+           WARN_ON_ONCE(rsp != rcu_state_p) ||
+           WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)) ||
+           rnp->qsmask != 0) {
                raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
                return;  /* Still need more quiescent states! */
        }