linux-kernel - [tip: sched/core] sched/debug: Fix fair_server_period

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Message-ID: <172302791517.2215.9583140780460140951.tip-bot2@tip-bot2>
Date: Wed, 07 Aug 2024 10:51:55 -0000
From: "tip-bot2 for Dan Carpenter" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Linux Kernel Functional Testing <lkft@...aro.org>,
 Arnd Bergmann <arnd@...nel.org>, Stephen Rothwell <sfr@...b.auug.org.au>,
 Dan Carpenter <dan.carpenter@...aro.org>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched/debug: Fix fair_server_period_max value

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     4ae0c2b91110dab6f4291c2c7f99dde60ecc97d8
Gitweb:        https://git.kernel.org/tip/4ae0c2b91110dab6f4291c2c7f99dde60ecc97d8
Author:        Dan Carpenter <dan.carpenter@...aro.org>
AuthorDate:    Thu, 01 Aug 2024 10:44:03 -05:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 07 Aug 2024 12:44:16 +02:00

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).

Closes: https://lore.kernel.org/all/CA+G9fYtE2GAbeqU+AOCffgo2oH0RTJUxU+=Pi3cFn4di_KgBAQ@mail.gmail.com/
Fixes: d741f297bcea ("sched/fair: Fair server interface")
Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
Reported-by: Arnd Bergmann <arnd@...nel.org>
Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/a936b991-e464-4bdf-94ab-08e25d364986@stanley.mountain
---
 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 e75914e..831a77a 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,