linux-kernel - [PATCH tip/core/rcu 04/22] rcu: Make rcu_report_unblock_qs

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Date:   Tue, 26 Jun 2018 10:10:30 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 04/22] 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@...ux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index a5dfb18d9b62..42ac3dd88fc5 100644
--- 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! */
 	}
-- 
2.17.1