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Sender: Ingo Molnar <mingo.kernel.org@gmail.com>
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
Message-Id: <20231006102518.2452758-4-mingo@kernel.org>
In-Reply-To: <20231006102518.2452758-1-mingo@kernel.org>
References: <20231006102518.2452758-1-mingo@kernel.org>
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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