linux-kernel - [PATCH] sched/deadline: fix one-bit signed bitfields to be unsigned

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Message-Id: <20171128203619.71430-1-jeffrey.t.kirsher@intel.com>
Date:   Tue, 28 Nov 2017 12:36:19 -0800
From:   Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:     mingo@...hat.com, peterz@...radead.org
Cc:     Jacob Keller <jacob.e.keller@...el.com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        nhorman@...hat.com, sassmann@...hat.com, jogreene@...hat.com,
        luca abeni <luca.abeni@...tannapisa.it>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: [PATCH] sched/deadline: fix one-bit signed bitfields to be unsigned

From: Jacob Keller <jacob.e.keller@...el.com>

Commit 799ba82de01e ("sched/deadline: Use C bitfields for the state
flags", 2017-10-10) introduced the use of C bitfields for these
variables. However, sparse complains about them:

./include/linux/sched.h:476:62: error: dubious one-bit signed bitfield
./include/linux/sched.h:477:62: error: dubious one-bit signed bitfield
./include/linux/sched.h:478:62: error: dubious one-bit signed bitfield
./include/linux/sched.h:479:62: error: dubious one-bit signed bitfield

This is because a one-bit signed bitfield can only hold the values 0 and
-1, which can cause problems if the program expects to be able to
represent the value positive 1.

In practice, this may not cause a bug since -1 would be considered
"true" in logical tests, however we should avoid the practice anyways.

Fixes: 799ba82de01e ("sched/deadline: Use C bitfields for the state flags", 2017-10-10)
Signed-off-by: Jacob Keller <jacob.e.keller@...el.com>
Cc: luca abeni <luca.abeni@...tannapisa.it>
Tested-by: Andrew Bowers <andrewx.bowers@...el.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
---
 include/linux/sched.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a5dc7c98b0a2..21991d668d35 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -473,10 +473,10 @@ struct sched_dl_entity {
 	 * conditions between the inactive timer handler and the wakeup
 	 * code.
 	 */
-	int				dl_throttled      : 1;
-	int				dl_boosted        : 1;
-	int				dl_yielded        : 1;
-	int				dl_non_contending : 1;
+	unsigned int			dl_throttled      : 1;
+	unsigned int			dl_boosted        : 1;
+	unsigned int			dl_yielded        : 1;
+	unsigned int			dl_non_contending : 1;
 
 	/*
 	 * Bandwidth enforcement timer. Each -deadline task has its
-- 
2.15.0