linux-kernel - [PATCH v11 15/20] timers: Check if timers base is handled already

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Date: Wed, 21 Feb 2024 10:05:43 +0100
From: Anna-Maria Behnsen <anna-maria@...utronix.de>
To: linux-kernel@...r.kernel.org
Cc: Peter Zijlstra <peterz@...radead.org>,
	John Stultz <jstultz@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Eric Dumazet <edumazet@...gle.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Arjan van de Ven <arjan@...radead.org>,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Rik van Riel <riel@...riel.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Sebastian Siewior <bigeasy@...utronix.de>,
	Giovanni Gherdovich <ggherdovich@...e.cz>,
	Lukasz Luba <lukasz.luba@....com>,
	"Gautham R . Shenoy" <gautham.shenoy@....com>,
	Srinivas Pandruvada <srinivas.pandruvada@...el.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	Christian Loehle <christian.loehle@....com>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: [PATCH v11 15/20] timers: Check if timers base is handled already

Due to the conversion of the NOHZ timer placement to a pull at expiry
time model, the per CPU timer bases with non pinned timers are no
longer handled only by the local CPU. In case a remote CPU already
expires the non pinned timers base of the local CPU, nothing more
needs to be done by the local CPU. A check at the begin of the expire
timers routine is required, because timer base lock is dropped before
executing the timer callback function.

This is a preparatory work, but has no functional impact right now.

Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
---
v10: s/cpu/CPU/ in commit message

v6: Drop double negation
---
 kernel/time/timer.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 52af50d00ae6..7b9f9ed25fc2 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -2240,6 +2240,9 @@ static inline void __run_timers(struct timer_base *base)
 
 	lockdep_assert_held(&base->lock);
 
+	if (base->running_timer)
+		return;
+
 	while (time_after_eq(jiffies, base->clk) &&
 	       time_after_eq(jiffies, base->next_expiry)) {
 		levels = collect_expired_timers(base, heads);
-- 
2.39.2