[tip: core/rcu] srcu: Early test SRCU polling start

[tip-bot2 for Frederic Weisbecker]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     0a580fa65cfa08a40af1a0a2cf73d100863e4981
Gitweb:        https://git.kernel.org/tip/0a580fa65cfa08a40af1a0a2cf73d100863e4981
Author:        Frederic Weisbecker <frederic@xxxxxxxxxx>
AuthorDate:    Wed, 14 Apr 2021 15:24:13 +02:00
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Wed, 12 May 2021 12:12:33 -07:00

srcu: Early test SRCU polling start

Place an early call to start_poll_synchronize_srcu() before the invocation
of call_srcu() on the same srcu_struct structure.

After the later call to srcu_barrier(), the completion of the
first grace period should be visible to a subsequent invocation of
poll_state_synchronize_srcu(), and if not, warn.

Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
Cc: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
Cc: Uladzislau Rezki <urezki@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/update.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index b95ae86..0aa118a 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -524,6 +524,7 @@ static void test_callback(struct rcu_head *r)
 }
 
 DEFINE_STATIC_SRCU(early_srcu);
+static unsigned long early_srcu_cookie;
 
 struct early_boot_kfree_rcu {
 	struct rcu_head rh;
@@ -536,8 +537,10 @@ static void early_boot_test_call_rcu(void)
 	struct early_boot_kfree_rcu *rhp;
 
 	call_rcu(&head, test_callback);
-	if (IS_ENABLED(CONFIG_SRCU))
+	if (IS_ENABLED(CONFIG_SRCU)) {
+		early_srcu_cookie = start_poll_synchronize_srcu(&early_srcu);
 		call_srcu(&early_srcu, &shead, test_callback);
+	}
 	rhp = kmalloc(sizeof(*rhp), GFP_KERNEL);
 	if (!WARN_ON_ONCE(!rhp))
 		kfree_rcu(rhp, rh);
@@ -563,6 +566,7 @@ static int rcu_verify_early_boot_tests(void)
 		if (IS_ENABLED(CONFIG_SRCU)) {
 			early_boot_test_counter++;
 			srcu_barrier(&early_srcu);
+			WARN_ON_ONCE(!poll_state_synchronize_srcu(&early_srcu, early_srcu_cookie));
 		}
 	}
 	if (rcu_self_test_counter != early_boot_test_counter) {