linux-kernel - [PATCH] sched/fair: avoid integer overflow warning for fair_server_period

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Message-Id: <20240807080032.2302853-1-arnd@kernel.org>
Date: Wed,  7 Aug 2024 10:00:08 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>
Cc: Arnd Bergmann <arnd@...db.de>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] sched/fair: avoid integer overflow warning for fair_server_period_max;

From: Arnd Bergmann <arnd@...db.de>

The clalculation of fair_server_period_max includes an integer overflow:

In file included from kernel/sched/build_utility.c:72:
kernel/sched/debug.c:341:57: error: integer overflow in expression of type 'long int' results in '-100663296' [-Werror=overflow]
  341 | static unsigned long fair_server_period_max = (1 << 22) * NSEC_PER_USEC; /* ~4 seconds */

Avoids this by using an unsigned constant to start with.

Fixes: d741f297bcea ("sched/fair: Fair server interface")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 kernel/sched/debug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 0148bc65d39c..242e7f264a0b 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -338,7 +338,7 @@ enum dl_param {
 	DL_PERIOD,
 };
 
-static unsigned long fair_server_period_max = (1 << 22) * NSEC_PER_USEC; /* ~4 seconds */
+static unsigned long fair_server_period_max = (1u << 22) * NSEC_PER_USEC; /* ~4 seconds */
 static unsigned long fair_server_period_min = (100) * NSEC_PER_USEC;     /* 100 us */
 
 static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubuf,
-- 
2.39.2