[PATCH] sched/deadline: Don't use dubious signed bitfields

[PATCH] sched/deadline: Don't use dubious signed bitfields

[Dan Carpenter]

It doesn't cause a run-time bug, but these bitfields should be unsigned.
When it's signed ->dl_throttled is set to either 0 or -1, instead of
0 and 1 as expected.  The sched.h file is included into tons of places
so Sparse generates a flood of warnings like this:

./include/linux/sched.h:477:54: error: dubious one-bit signed bitfield

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 0f897dfc195e..105eaff8a5e7 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -474,10 +474,10 @@ 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: [PATCH] sched/deadline: Don't use dubious signed bitfields

[Luca Abeni]

Hi,

On Fri, 13 Oct 2017 10:01:22 +0300
Dan Carpenter <dan.carpenter@oracle.com> wrote:

> It doesn't cause a run-time bug, but these bitfields should be unsigned.
> When it's signed ->dl_throttled is set to either 0 or -1, instead of
> 0 and 1 as expected.  The sched.h file is included into tons of places
> so Sparse generates a flood of warnings like this:
> 
> ./include/linux/sched.h:477:54: error: dubious one-bit signed bitfield
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

I did not notice any issue when testing, but if "unsigned int" is the
common practice for bitfields, I agree with the change.

Reviewed-by: Luca Abeni <luca.abeni@santannapisa.it>


			Thanks,
				Luca
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 0f897dfc195e..105eaff8a5e7 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -474,10 +474,10 @@ 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: [PATCH] sched/deadline: Don't use dubious signed bitfields

[Dan Carpenter]

On Fri, Oct 13, 2017 at 09:36:06AM +0200, Luca Abeni wrote:
> Hi,
> 
> On Fri, 13 Oct 2017 10:01:22 +0300
> Dan Carpenter <dan.carpenter@oracle.com> wrote:
> 
> > It doesn't cause a run-time bug, but these bitfields should be unsigned.
> > When it's signed ->dl_throttled is set to either 0 or -1, instead of
> > 0 and 1 as expected.  The sched.h file is included into tons of places
> > so Sparse generates a flood of warnings like this:
> > 
> > ./include/linux/sched.h:477:54: error: dubious one-bit signed bitfield
> > 
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> 
> I did not notice any issue when testing

Correct.  It would only cause a bug if we had a condition like:

	if (foo->dl_throttled = 1) {

That would be impossible because ->dl_throttled = -1, but since the
conditions are all in the form:

	if (foo->dl_throttled) {

Then that works for both 1 and -1.

regards,
dan carpenter