linux-kernel - [PATCH 3/3] Revert "rcu/nocb: Fix rcuog wake-up from offline softirq"

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Message-ID: <20241218165008.37820-4-frederic@kernel.org>
Date: Wed, 18 Dec 2024 17:50:08 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	vlad.wing@...il.com,
	rcu@...r.kernel.org,
	boqun.feng@...il.com,
	joel@...lfernandes.org,
	neeraj.upadhyay@....com,
	urezki@...il.com,
	qiang.zhang1211@...il.com,
	Cheng-Jui.Wang@...iatek.com,
	leitao@...ian.org,
	kernel-team@...a.com,
	Usama Arif <usamaarif642@...il.com>,
	paulmck@...nel.org,
	Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: [PATCH 3/3] Revert "rcu/nocb: Fix rcuog wake-up from offline softirq"

This reverts commit f7345ccc62a4b880cf76458db5f320725f28e400.

swake_up_one_online() has been removed because hrtimers can now assign
a proper online target to hrtimers queued from offline CPUs. Therefore
remove the related hackery.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 kernel/rcu/tree_nocb.h | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index a43141a1b3a5..a03fc19abde7 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -554,19 +554,13 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
 			rcu_nocb_unlock(rdp);
 			wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_LAZY,
 					   TPS("WakeLazy"));
-		} else if (!irqs_disabled_flags(flags) && cpu_online(rdp->cpu)) {
+		} else if (!irqs_disabled_flags(flags)) {
 			/* ... if queue was empty ... */
 			rcu_nocb_unlock(rdp);
 			wake_nocb_gp(rdp, false);
 			trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
 					    TPS("WakeEmpty"));
 		} else {
-			/*
-			 * Don't do the wake-up upfront on fragile paths.
-			 * Also offline CPUs can't call swake_up_one_online() from
-			 * (soft-)IRQs. Rely on the final deferred wake-up from
-			 * rcutree_report_cpu_dead()
-			 */
 			rcu_nocb_unlock(rdp);
 			wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE,
 					   TPS("WakeEmptyIsDeferred"));
-- 
2.46.0