linux-kernel - [PATCH rcu 05/25] rcutorture: Verify RCU reader prevents full polling from completing

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Date:   Wed, 31 Aug 2022 11:11:50 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org, "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 05/25] rcutorture: Verify RCU reader prevents full polling from completing

This commit adds a test to rcu_torture_writer() that verifies that a
->get_gp_state_full() and ->poll_gp_state_full() polled grace-period
sequence does not claim that a grace period elapsed within the confines
of the corresponding read-side critical section.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/rcutorture.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index f2564c7633a8a..050f4d0a987ff 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1309,6 +1309,8 @@ rcu_torture_writer(void *arg)
 			atomic_inc(&rcu_torture_wcount[i]);
 			WRITE_ONCE(old_rp->rtort_pipe_count,
 				   old_rp->rtort_pipe_count + 1);
+
+			// Make sure readers block polled grace periods.
 			if (cur_ops->get_gp_state && cur_ops->poll_gp_state) {
 				idx = cur_ops->readlock();
 				cookie = cur_ops->get_gp_state();
@@ -1325,9 +1327,20 @@ rcu_torture_writer(void *arg)
 				}
 				cur_ops->readunlock(idx);
 			}
-			if (cur_ops->get_gp_completed_full && cur_ops->poll_gp_state_full) {
-				cur_ops->get_gp_completed_full(&cookie_full);
-				WARN_ON_ONCE(!cur_ops->poll_gp_state_full(&cookie_full));
+			if (cur_ops->get_gp_state_full && cur_ops->poll_gp_state_full) {
+				idx = cur_ops->readlock();
+				cur_ops->get_gp_state_full(&cookie_full);
+				WARN_ONCE(cur_ops->poll_gp_state_full(&cookie_full),
+					  "%s: Cookie check 5 failed %s(%d) online %*pbl\n",
+					  __func__,
+					  rcu_torture_writer_state_getname(),
+					  rcu_torture_writer_state,
+					  cpumask_pr_args(cpu_online_mask));
+				if (cur_ops->get_gp_completed_full) {
+					cur_ops->get_gp_completed_full(&cookie_full);
+					WARN_ON_ONCE(!cur_ops->poll_gp_state_full(&cookie_full));
+				}
+				cur_ops->readunlock(idx);
 			}
 			switch (synctype[torture_random(&rand) % nsynctypes]) {
 			case RTWS_DEF_FREE:
-- 
2.31.1.189.g2e36527f23