linux-kernel - Re: New sparse warnings from sched.h

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Message-ID: <20171115145445.GA319@bombadil.infradead.org>
Date:   Wed, 15 Nov 2017 06:54:45 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     luca abeni <luca.abeni@...tannapisa.it>,
        Peter Zijlstra <peterz@...radead.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: New sparse warnings from sched.h

On Wed, Nov 15, 2017 at 09:27:43AM +0100, Ingo Molnar wrote:
> * Matthew Wilcox <willy@...radead.org> wrote:
> > 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
> 
> Mind sending a proper patch with a SOB once it's tested?

I'd be more than happy to do that.  I have no idea what this code is,
what it's used for, or how to test it, so I'll have to rely on somebody
else to test it.