[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

[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

[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

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

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

[tip-bot for Dan Carpenter]

Commit-ID:  aa5222e92f8000ed3c1c38dddf11c83222aadfb3
Gitweb:     https://git.kernel.org/tip/aa5222e92f8000ed3c1c38dddf11c83222aadfb3
Author:     Dan Carpenter <dan.carpenter@oracle.com>
AuthorDate: Fri, 13 Oct 2017 10:01:22 +0300
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 21 Nov 2017 09:25:01 +0100

sched/deadline: Don't use dubious signed bitfields

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

Reported-by: Matthew Wilcox <willy@infradead.org>
Reported-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Luca Abeni <luca.abeni@santannapisa.it>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-janitors@vger.kernel.org
Cc: luca abeni <luca.abeni@santannapisa.it>
Link: http://lkml.kernel.org/r/20171013070121.dzcncojuj2f4utij@mwanda
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 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 a5dc7c9..21991d6 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