New sparse warnings from sched.h

New sparse warnings from sched.h

[Matthew Wilcox]

commit 799ba82de01e7543f6b2042e1a739f3a20255f23
Author: luca abeni <luca.abeni@santannapisa.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

Re: New sparse warnings from sched.h

[Ingo Molnar]

* Matthew Wilcox <willy@infradead.org> wrote:

> 
> commit 799ba82de01e7543f6b2042e1a739f3a20255f23
> Author: luca abeni <luca.abeni@santannapisa.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?

Thanks,

	Ingo

Re: New sparse warnings from sched.h

[luca abeni]

Hi,

On Tue, 14 Nov 2017 12:41:35 -0800
Matthew Wilcox <willy@infradead.org> wrote:

> commit 799ba82de01e7543f6b2042e1a739f3a20255f23
> Author: luca abeni <luca.abeni@santannapisa.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):
[...]

I think Dan Carpenter sent a similar patch (and I replied agreeing with
it).

I believe in this particular case signed integers are safe, but if
"unsigned int" is the preferred style in the kernel I agree with the
change.


			Thanks,
				Luca

> 
> 
> 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

Re: New sparse warnings from sched.h

[Matthew Wilcox]

On Wed, Nov 15, 2017 at 09:27:43AM +0100, Ingo Molnar wrote:
> * Matthew Wilcox <willy@infradead.org> wrote:
> > commit 799ba82de01e7543f6b2042e1a739f3a20255f23
> > Author: luca abeni <luca.abeni@santannapisa.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.

Re: New sparse warnings from sched.h

[Ingo Molnar]

* Matthew Wilcox <willy@infradead.org> wrote:

> On Wed, Nov 15, 2017 at 09:27:43AM +0100, Ingo Molnar wrote:
> > * Matthew Wilcox <willy@infradead.org> wrote:
> > > commit 799ba82de01e7543f6b2042e1a739f3a20255f23
> > > Author: luca abeni <luca.abeni@santannapisa.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.

Oh, I thought you wanted to test whether it fixes the Sparse bug.

Converting these bitfields from signed to unsigned should have no effect on the 
deadline scheduler.

I.e. I basically only need your Signed-off-by.

Thnaks,

	Ingo