linux-kernel - New sparse warnings from sched.h

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Message-ID: <20171114204135.GA23685@bombadil.infradead.org>
Date:   Tue, 14 Nov 2017 12:41:35 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     luca abeni <luca.abeni@...tannapisa.it>,
        Peter Zijlstra <peterz@...radead.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org
Subject: New sparse warnings from sched.h


commit 799ba82de01e7543f6b2042e1a739f3a20255f23
Author: luca abeni <luca.abeni@...tannapisa.it>
Date:   Thu Sep 7 12:09:31 2017 +0200

    sched/deadline: Use C bitfields for the state flags
    
    Ask the compiler to use a single bit for storing true / false values,
    instead of wasting the size of a whole int value.
    Tested with gcc 5.4.0 on x86_64, and the compiler produces the expected
    Assembly (similar to the Assembly code generated when explicitly accessing
    the bits with bitmasks, "&" and "|").

produces four warnings from sparse for every file which includes sched.h:

./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 seems like the trivial fix (untested):


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