linux-kernel - [PATCH rcu 08/11] rcutorture: Update ->extendables check for lazy preemption

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Message-Id: <20250225035516.26443-9-boqun.feng@gmail.com>
Date: Mon, 24 Feb 2025 19:55:13 -0800
From: Boqun Feng <boqun.feng@...il.com>
To: rcu@...r.kernel.org
Cc: "Paul E. McKenney" <paulmck@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,	Boqun Feng <boqun.feng@...il.com>,
	Uladzislau Rezki <urezki@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>,	Davidlohr Bueso <dave@...olabs.net>,
	Ingo Molnar <mingo@...hat.com>,	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Ben Segall <bsegall@...gle.com>,	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,	Shuah Khan <shuah@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Clark Williams <clrkwllms@...nel.org>,	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,	linux-kselftest@...r.kernel.org,
	linux-rt-devel@...ts.linux.dev,	Ankur Arora <ankur.a.arora@...cle.com>
Subject: [PATCH rcu 08/11] rcutorture: Update ->extendables check for lazy preemption

The rcutorture_one_extend_check() function's second last check assumes
that "preempt_count() & PREEMPT_MASK" is non-zero only if
RCUTORTURE_RDR_PREEMPT or RCUTORTURE_RDR_SCHED bit is set.

This works for preemptible RCU and for non-preemptible RCU running in
a non-preemptible kernel.  But it fails for non-preemptible RCU running
in a preemptible kernel because then rcu_read_lock() is just
preempt_disable(), which increases preempt count.

This commit therefore adjusts this check to take into account the case
fo non-preemptible RCU running in a preemptible kernel.

Reviewed-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
 kernel/rcu/rcutorture.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 280bff706017..4cae119dece8 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1901,8 +1901,16 @@ static void rcutorture_one_extend_check(char *s, int curstate, int new, int old,
 	WARN_ONCE(cur_ops->extendables &&
 		  !(curstate & (RCUTORTURE_RDR_BH | RCUTORTURE_RDR_RBH)) &&
 		  (preempt_count() & SOFTIRQ_MASK), ROEC_ARGS);
-	WARN_ONCE(cur_ops->extendables &&
-		  !(curstate & (RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED)) &&
+
+	/*
+	 * non-preemptible RCU in a preemptible kernel uses preempt_disable()
+	 * as rcu_read_lock().
+	 */
+	mask = RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED;
+	if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
+		mask |= RCUTORTURE_RDR_RCU_1 | RCUTORTURE_RDR_RCU_2;
+
+	WARN_ONCE(cur_ops->extendables && !(curstate & mask) &&
 		  (preempt_count() & PREEMPT_MASK), ROEC_ARGS);
 
 	/*
-- 
2.39.5 (Apple Git-154)