From: Paul E. McKenney <paulmck@kernel.org>
Date: Mon, 23 Jun 2025 19:39:55 +0000 (-0700)
Subject: rcu: Document that rcu_barrier() hurries lazy callbacks
X-Git-Tag: v6.18-rc1~86^2~2^2~5
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=faab3ae329a6efb96995aeb72a68a99f664fed38;p=thirdparty%2Fkernel%2Flinux.git

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@kernel.org>
---

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 8eff357b0436b..1291e0761d70a 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)
 {