linux-kernel - [PATCH rcu 32/32] rcu-tasks: Use delayed_work to delay rcu_tasks_verify_self

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Date:   Mon, 20 Jun 2022 15:54:11 -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, Waiman Long <longman@...hat.com>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 32/32] rcu-tasks: Use delayed_work to delay rcu_tasks_verify_self_tests()

From: Waiman Long <longman@...hat.com>

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 delaying
other late_initcall's queued after it by a second or more.  Fix this by
instead using delayed_work to repeat the verification check.

Fixes: 2585014188d5 ("rcu-tasks: Be more patient for RCU Tasks boot-time testing")
Signed-off-by: Waiman Long <longman@...hat.com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tasks.h | 37 ++++++++++++++++++++++++++++++++-----
 1 file changed, 32 insertions(+), 5 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index fcbd0ec33c866..83c7e6620d403 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 +1852,38 @@ static int rcu_tasks_verify_self_tests(void)
 				ret = -1;
 				break;
 			}
-			schedule_timeout_uninterruptible(1);
+			ret = 1;
+			break;
 		}
 	}
-
-	if (ret)
-		WARN_ON(1);
+	WARN_ON(ret < 0);
 
 	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 */
-- 
2.31.1.189.g2e36527f23