linux-kernel - [PATCH 03/10] cpuidle: Report illegal tick stopped while polling

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Date:   Fri, 11 Aug 2023 19:00:42 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: [PATCH 03/10] cpuidle: Report illegal tick stopped while polling

poll_idle() can't be called while the tick is stopped because it enables
interrupts and only polls on TIF_NEED_RESCHED, which doesn't tell if an
interrupt queues a timer that would require a tick re-programming.

There is no point anyway to poll with the tick stopped so add a check
to make sure it never happens.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 drivers/cpuidle/poll_state.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
index 9b6d90a72601..009f46f121ae 100644
--- a/drivers/cpuidle/poll_state.c
+++ b/drivers/cpuidle/poll_state.c
@@ -7,6 +7,7 @@
 #include <linux/sched.h>
 #include <linux/sched/clock.h>
 #include <linux/sched/idle.h>
+#include <linux/tick.h>
 
 #define POLL_IDLE_RELAX_COUNT	200
 
@@ -19,6 +20,13 @@ static int __cpuidle poll_idle(struct cpuidle_device *dev,
 
 	dev->poll_time_limit = false;
 
+	/*
+	 * This re-enables IRQs and only polls on TIF_NEED_RESCHED.
+	 * A timer queued by an interrupt here may go unnoticed if
+	 * the tick is stopped.
+	 */
+	WARN_ON_ONCE(tick_nohz_tick_stopped());
+
 	raw_local_irq_enable();
 	if (!current_set_polling_and_test()) {
 		unsigned int loop_count = 0;
-- 
2.34.1