linux-kernel - [PATCH 1/3] rcu: Document that rcu_barrier() hurries lazy callbacks

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Message-Id: <20250816000149.2622447-1-paulmck@kernel.org>
Date: Fri, 15 Aug 2025 17:01:47 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	rostedt@...dmis.org,
	"Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH 1/3] rcu: Document that rcu_barrier() hurries lazy callbacks

This commit adds to the rcu_barrier() kerneldoc header stating that this
function hurries lazy callbacks and that it does not normally result in
additional RCU grace periods.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tree.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 8eff357b0436be..1291e0761d70ab 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3800,6 +3800,11 @@ static void rcu_barrier_handler(void *cpu_in)
  * to complete.  For example, if there are no RCU callbacks queued anywhere
  * in the system, then rcu_barrier() is within its rights to return
  * immediately, without waiting for anything, much less an RCU grace period.
+ * In fact, rcu_barrier() will normally not result in any RCU grace periods
+ * beyond those that were already destined to be executed.
+ *
+ * In kernels built with CONFIG_RCU_LAZY=y, this function also hurries all
+ * pending lazy RCU callbacks.
  */
 void rcu_barrier(void)
 {
-- 
2.40.1