linux-kernel - [PATCH] sched/debug: Fix fair_server_period

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Message-ID: <a936b991-e464-4bdf-94ab-08e25d364986@stanley.mountain>
Date: Thu, 1 Aug 2024 10:44:03 -0500
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Daniel Bristot de Oliveira <bristot@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	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,
	Naresh Kamboju <naresh.kamboju@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Anders Roxell <anders.roxell@...aro.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: [PATCH] sched/debug: Fix fair_server_period_max value

This code has an integer overflow or sign extension bug which was caught
by gcc-13:

  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 */

The result is that "fair_server_period_max" is set to 0xfffffffffa000000
(585 years) instead of instead of 0xfa000000 (4 seconds) that was
intended.

Fix this by changing the type to shift from (1 << 22) to (1UL << 22).

Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
Closes: https://lore.kernel.org/all/CA+G9fYtE2GAbeqU+AOCffgo2oH0RTJUxU+=Pi3cFn4di_KgBAQ@mail.gmail.com/
Fixes: d741f297bcea ("sched/fair: Fair server interface")
Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
---
 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..845b79238398 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 = (1UL << 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,
-- 
2.43.0