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From: Ingo Molnar <mingo@kernel.org>
To: linux-kernel@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Valentin Schneider <vschneid@redhat.com>,
	Frederic Weisbecker <frederic@kernel.org>,
	Joel Fernandes <joel@joelfernandes.org>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: [PATCH 3/3] sched/nohz: Remove weird error handling from find_new_ilb()
Date: Fri,  6 Oct 2023 12:25:18 +0200	[thread overview]
Message-ID: <20231006102518.2452758-4-mingo@kernel.org> (raw)
In-Reply-To: <20231006102518.2452758-1-mingo@kernel.org>

find_new_ilb() returns nr_cpu_ids on failure - which is a weird
choice in itself: not only is it a global variable, it is
a +1 out of bounds CPU index...

Its only user, kick_ilb(), then checks the return against nr_cpu_ids
to decide to return.

Instead of this, use a standard -1 return on failure to find an
idle CPU, as the argument is signed already.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: linux-kernel@vger.kernel.org
---
 kernel/sched/fair.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d4e90d15bd77..dad60576cf56 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11572,7 +11572,7 @@ static inline int find_new_ilb(void)
 			return ilb_cpu;
 	}
 
-	return nr_cpu_ids;
+	return -1;
 }
 
 /*
@@ -11593,8 +11593,7 @@ static void kick_ilb(unsigned int flags)
 		nohz.next_balance = jiffies+1;
 
 	ilb_cpu = find_new_ilb();
-
-	if (ilb_cpu >= nr_cpu_ids)
+	if (ilb_cpu < 0)
 		return;
 
 	/*
-- 
2.39.2


  parent reply	other threads:[~2023-10-06 10:25 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-10-06 10:25 [PATCH 0/3] sched/nohz: Misc minor cleanups to the NOHZ idle balancing code Ingo Molnar
2023-10-06 10:25 ` [PATCH 1/3] sched/nohz: Update idle load-balancing (ILB) comments Ingo Molnar
2023-10-09 10:26   ` [tip: sched/core] " tip-bot2 for Ingo Molnar
2023-10-09 15:12   ` [PATCH 1/3] " Valentin Schneider
2023-10-06 10:25 ` [PATCH 2/3] sched/nohz: Use consistent variable names in find_new_ilb() and kick_ilb() Ingo Molnar
2023-10-09 10:26   ` [tip: sched/core] " tip-bot2 for Ingo Molnar
2023-10-09 15:12   ` [PATCH 2/3] " Valentin Schneider
2023-10-06 10:25 ` Ingo Molnar [this message]
2023-10-06 10:38   ` [PATCH 3/3] sched/nohz: Remove weird error handling from find_new_ilb() Peter Zijlstra
2023-10-06 11:01     ` Ingo Molnar
2023-10-09 15:11       ` Valentin Schneider
2023-10-09 10:26   ` [tip: sched/core] sched/nohz: Remove unnecessarily complex error handling pattern " tip-bot2 for Ingo Molnar
2023-10-08 16:56 ` [PATCH 0/3] sched/nohz: Misc minor cleanups to the NOHZ idle balancing code Joel Fernandes

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