linux-kernel - [PATCH-rcu] rcu-tasks: Use delayed_work to delay rcu_tasks_verify_self

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Date:   Tue, 14 Jun 2022 08:06:20 -0400
From:   Waiman Long <longman@...hat.com>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Uladzislau Rezki (Sony)" <urezki@...il.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH-rcu] rcu-tasks: Use delayed_work to delay rcu_tasks_verify_self_tests()

Commit 2585014188d5 ("rcu-tasks: Be more patient for RCU Tasks
boot-time testing") fixes false positive rcu_tasks verification check
failure by repeating the test once every second until timeout using
schedule_timeout_uninterruptible().

Since rcu_tasks_verify_selft_tests() is called from do_initcalls()
as a late_initcall, this has the undesirable side effect of perhaps
delaying other late_initcall's queued after it by a second or more.
Fix this by using delayed_work to repeat the verification check instead.

Fixes: 2585014188d5 ("rcu-tasks: Be more patient for RCU Tasks boot-time testing")
Signed-off-by: Waiman Long <longman@...hat.com>
---
 kernel/rcu/tasks.h | 35 ++++++++++++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index fcbd0ec33c86..e151cd5ae2bc 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1832,6 +1832,11 @@ static void rcu_tasks_initiate_self_tests(void)
 #endif
 }
 
+/*
+ * Return:  0 - test passed
+ *	    1 - test failed, but have not timed out yet
+ *	   -1 - test failed and timed out
+ */
 static int rcu_tasks_verify_self_tests(void)
 {
 	int ret = 0;
@@ -1847,16 +1852,40 @@ static int rcu_tasks_verify_self_tests(void)
 				ret = -1;
 				break;
 			}
-			schedule_timeout_uninterruptible(1);
+			ret = 1;
+			break;
 		}
 	}
 
-	if (ret)
+	if (ret < 0)
 		WARN_ON(1);
 
 	return ret;
 }
-late_initcall(rcu_tasks_verify_self_tests);
+
+/*
+ * Repeat the rcu_tasks_verify_self_tests() call once every second until the
+ * test passes or has timed out.
+ */
+static struct delayed_work rcu_tasks_verify_work;
+static void rcu_tasks_verify_work_fn(struct work_struct *work __maybe_unused)
+{
+	int ret = rcu_tasks_verify_self_tests();
+
+	if (ret <= 0)
+		return;
+
+	/* Test fails but not timed out yet, reschedule another check */
+	schedule_delayed_work(&rcu_tasks_verify_work, HZ);
+}
+
+static int rcu_tasks_verify_schedule_work(void)
+{
+	INIT_DELAYED_WORK(&rcu_tasks_verify_work, rcu_tasks_verify_work_fn);
+	rcu_tasks_verify_work_fn(NULL);
+	return 0;
+}
+late_initcall(rcu_tasks_verify_schedule_work);
 #else /* #ifdef CONFIG_PROVE_RCU */
 static void rcu_tasks_initiate_self_tests(void) { }
 #endif /* #else #ifdef CONFIG_PROVE_RCU */
-- 
2.31.1