linux-kernel - [PATCH v2] sched/deadline: Use unsigned type for the state flags

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Message-ID: <nycvar.YFH.7.76.1711211259180.11505@cbobk.fhfr.pm>
Date:   Tue, 21 Nov 2017 13:00:47 +0100 (CET)
From:   Jiri Kosina <jikos@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
cc:     luca abeni <luca.abeni@...tannapisa.it>,
        Peter Zijlstra <peterz@...radead.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Juri Lelli <juri.lelli@....com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Mike Galbraith <efault@....de>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] sched/deadline: Use unsigned type for the state flags

Commit

        799ba82de01e ("sched/deadline: Use C bitfields for the state flags")

converted state flags into one-bit signed int. Signed one-bit type can be
either 0 or -1, which is going to cause a problem once 1 is assigned to
it and then the value later tested against 1.

The current code is okay, as all the checks are (non-)zero check, but I believe
that we'd rather be safe than sorry here; remove the fragility by converting
the state flags to unsigned int, where 1 actually really is 1.

This also silences annoying sparse complaints about this very issue when
compiling any code that includes sched.h.

Fixes: 799ba82de01e ("sched/deadline: Use C bitfields for the state flags")
Cc: luca abeni <luca.abeni@...tannapisa.it>
Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: Juri Lelli <juri.lelli@....com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
Cc: Mike Galbraith <efault@....de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Jiri Kosina <jkosina@...e.cz>
---

v2: switch over to unsisgned int from bool, as asked for by Thomas. Feel 
    free to pick either of the versions

 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..b634da8a35a3 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
-- 
Jiri Kosina
SUSE Labs