linux-kernel - [PATCH rcu 3/9] sched: update __cond_resched comment about RCU quiescent states

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Message-Id: <20250116201327.3782963-3-paulmck@kernel.org>
Date: Thu, 16 Jan 2025 12:13:21 -0800
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,
	Ankur Arora <ankur.a.arora@...cle.com>,
	Frederic Weisbecker <frederic@...nel.org>,
	"Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 3/9] sched: update __cond_resched comment about RCU quiescent states

From: Ankur Arora <ankur.a.arora@...cle.com>

Update comment in __cond_resched() clarifying how urgently needed
quiescent state are provided.

Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/sched/core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 95e40895a5190..b0f7ffcc46a66 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7281,7 +7281,7 @@ int __sched __cond_resched(void)
 		return 1;
 	}
 	/*
-	 * In preemptible kernels, ->rcu_read_lock_nesting tells the tick
+	 * In PREEMPT_RCU kernels, ->rcu_read_lock_nesting tells the tick
 	 * whether the current CPU is in an RCU read-side critical section,
 	 * so the tick can report quiescent states even for CPUs looping
 	 * in kernel context.  In contrast, in non-preemptible kernels,
@@ -7290,6 +7290,8 @@ int __sched __cond_resched(void)
 	 * RCU quiescent state.  Therefore, the following code causes
 	 * cond_resched() to report a quiescent state, but only when RCU
 	 * is in urgent need of one.
+	 * A third case, preemptible, but non-PREEMPT_RCU provides for
+	 * urgently needed quiescent states via rcu_flavor_sched_clock_irq().
 	 */
 #ifndef CONFIG_PREEMPT_RCU
 	rcu_all_qs();
-- 
2.40.1