[PATCH v3 7/7] rcu: Add CONFIG_RCU_SR_NORMAL_DEBUG_GP

["Uladzislau Rezki (Sony)" <urezki@gmail.com>]

This option enables additional debugging for detecting a grace
period incompletion for synchronize_rcu() users. If a GP is not
fully passed for any user, the warning message is emitted.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
 kernel/rcu/Kconfig.debug | 12 ++++++++++++
 kernel/rcu/tree.c        |  7 +++++--
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 2984de629f74..3d44106ca1f0 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -143,4 +143,16 @@ config RCU_STRICT_GRACE_PERIOD
 	  when looking for certain types of RCU usage bugs, for example,
 	  too-short RCU read-side critical sections.
 
+config RCU_SR_NORMAL_DEBUG_GP
+	bool "Debug synchronize_rcu() callers for a grace period completion"
+	depends on DEBUG_KERNEL && RCU_EXPERT
+	default n
+	help
+	  This option enables additional debugging for detecting a grace
+	  period incompletion for synchronize_rcu() users. If a GP is not
+	  fully passed for any user, the warning message is emitted.
+
+	  Say Y here if you want to enable such debugging
+	  Say N if you are unsure.
+
 endmenu # "RCU Debugging"
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index c0d3e46730e8..421bce4b8dd7 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1547,7 +1547,8 @@ static void rcu_sr_normal_complete(struct llist_node *node)
 		(struct rcu_head *) node, struct rcu_synchronize, head);
 	unsigned long oldstate = (unsigned long) rs->head.func;
 
-	WARN_ONCE(!rcu_gp_is_expedited() && !poll_state_synchronize_rcu(oldstate),
+	WARN_ONCE(IS_ENABLED(CONFIG_RCU_SR_NORMAL_DEBUG_GP) &&
+		!poll_state_synchronize_rcu(oldstate),
 		"A full grace period is not passed yet: %lu",
 		rcu_seq_diff(get_state_synchronize_rcu(), oldstate));
 
@@ -3822,7 +3823,9 @@ static void synchronize_rcu_normal(void)
 	 * This code might be preempted, therefore take a GP
 	 * snapshot before adding a request.
 	 */
-	rs.head.func = (void *) get_state_synchronize_rcu();
+	if (IS_ENABLED(CONFIG_RCU_SR_NORMAL_DEBUG_GP))
+		rs.head.func = (void *) get_state_synchronize_rcu();
+
 	rcu_sr_normal_add_req(&rs);
 
 	/* Kick a GP and start waiting. */
-- 
2.39.2