[PATCH] futex: Fix a faulty comment.

[PATCH] futex: Fix a faulty comment.

[6812skiii]

From: Jangwoong Kim <6812skiii@gmail.com>

We return 1, not the index of futex woken up.

Signed-off-by: Jangwoong Kim <6812skiii@gmail.com>
---
 kernel/futex/waitwake.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/futex/waitwake.c b/kernel/futex/waitwake.c
index 4ce0923f1ce3..d148e5d4956b 100644
--- a/kernel/futex/waitwake.c
+++ b/kernel/futex/waitwake.c
@@ -455,8 +455,8 @@ static int futex_wait_multiple_setup(struct futex_vector *vs, int count, int *wo
 
 		/*
 		 * Even if something went wrong, if we find out that a futex
-		 * was woken, we don't return error and return this index to
-		 * userspace
+		 * was woken, we don't return error and make userspace aware
+		 * of this by returning 1.
 		 */
 		*woken = unqueue_multiple(vs, i);
 		if (*woken >= 0)
-- 
2.25.1

Re: [PATCH] futex: Fix a faulty comment.

[André Almeida]

Hi Jangwoong,

Thanks for your patch! However...

Às 15:14 de 04/12/21, 6812skiii@gmail.com escreveu:
> From: Jangwoong Kim <6812skiii@gmail.com>
> 
> We return 1, not the index of futex woken up.
> 
> Signed-off-by: Jangwoong Kim <6812skiii@gmail.com>
> ---
>  kernel/futex/waitwake.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/futex/waitwake.c b/kernel/futex/waitwake.c
> index 4ce0923f1ce3..d148e5d4956b 100644
> --- a/kernel/futex/waitwake.c
> +++ b/kernel/futex/waitwake.c
> @@ -455,8 +455,8 @@ static int futex_wait_multiple_setup(struct futex_vector *vs, int count, int *wo
>  
>  		/*
>  		 * Even if something went wrong, if we find out that a futex
> -		 * was woken, we don't return error and return this index to
> -		 * userspace
> +		 * was woken, we don't return error and make userspace aware
> +		 * of this by returning 1.

We return to userspace the value at *woken, so your fix is wrong. Have a
look at futex_wait_multiple():

		ret = futex_wait_multiple_setup(vs, count, &hint);
		if (ret) {
			if (ret > 0) {
				/* A futex was woken during setup */
				ret = hint;
			}
			return ret;
		}

When we return 1 at futex_wait_multiple_setup(), we end up returning the
hint/woken value to userspace.

Let me know if you have questions.

	André

Re: [PATCH] futex: Fix a faulty comment.

[Jangwoong Kim]

Hi André.

That patch was definitely wrong, I apologize.

However, since futex_wait_multiple_setup() sets the last index of
futex that was woken up,
shouldn't the comment be modified as below?

If so, I will resend a patch.

                /*
-                * Even if something went wrong, if we find out that a futex
-                * was woken, we don't return error and return this index to
-                * userspace
+                * Even if something went wrong, if we find out that any futex
+                * was woken, we don't return error and return the last index
+                * awoken to userspace
                 */
                *woken = unqueue_multiple(vs, i);
                if (*woken >= 0)

I sent the patch because I thought this was important enough to be corrected.

Let me know If this is not crucial enough to be patched, so I won't
keep sending comment-fixing patches.

Thank you.
Jangwoong Kim.

2021년 12월 6일 (월) 오후 9:12, André Almeida <andrealmeid@collabora.com>님이 작성:
>
> Hi Jangwoong,
>
> Thanks for your patch! However...
>
> Às 15:14 de 04/12/21, 6812skiii@gmail.com escreveu:
> > From: Jangwoong Kim <6812skiii@gmail.com>
> >
> > We return 1, not the index of futex woken up.
> >
> > Signed-off-by: Jangwoong Kim <6812skiii@gmail.com>
> > ---
> >  kernel/futex/waitwake.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/futex/waitwake.c b/kernel/futex/waitwake.c
> > index 4ce0923f1ce3..d148e5d4956b 100644
> > --- a/kernel/futex/waitwake.c
> > +++ b/kernel/futex/waitwake.c
> > @@ -455,8 +455,8 @@ static int futex_wait_multiple_setup(struct futex_vector *vs, int count, int *wo
> >
> >               /*
> >                * Even if something went wrong, if we find out that a futex
> > -              * was woken, we don't return error and return this index to
> > -              * userspace
> > +              * was woken, we don't return error and make userspace aware
> > +              * of this by returning 1.
>
> We return to userspace the value at *woken, so your fix is wrong. Have a
> look at futex_wait_multiple():
>
>                 ret = futex_wait_multiple_setup(vs, count, &hint);
>                 if (ret) {
>                         if (ret > 0) {
>                                 /* A futex was woken during setup */
>                                 ret = hint;
>                         }
>                         return ret;
>                 }
>
> When we return 1 at futex_wait_multiple_setup(), we end up returning the
> hint/woken value to userspace.
>
> Let me know if you have questions.
>
>         André

Re: [PATCH] futex: Fix a faulty comment.

[André Almeida]

Hi Jangwoong,

Please don't top post when replying to emails in this list (read more
here: https://www.mediawiki.org/wiki/Mailing_list_etiquette)

Às 14:44 de 06/12/21, Jangwoong Kim escreveu:
> Hi André.
> 
> That patch was definitely wrong, I apologize.
> 
> However, since futex_wait_multiple_setup() sets the last index of
> futex that was woken up,
> shouldn't the comment be modified as below?
> 
> If so, I will resend a patch.
> 
>                 /*
> -                * Even if something went wrong, if we find out that a futex
> -                * was woken, we don't return error and return this index to
> -                * userspace
> +                * Even if something went wrong, if we find out that any futex
> +                * was woken, we don't return error and return the last index
> +                * awoken to userspace

Indeed, this is more correct. You can send a patch to clarify this comment.

>                  */
>                 *woken = unqueue_multiple(vs, i);
>                 if (*woken >= 0)
> 
> I sent the patch because I thought this was important enough to be corrected.
> 
> Let me know If this is not crucial enough to be patched, so I won't
> keep sending comment-fixing patches.
> 
> Thank you.
> Jangwoong Kim.
> 
> 2021년 12월 6일 (월) 오후 9:12, André Almeida <andrealmeid@collabora.com>님이 작성:
>>
>> Hi Jangwoong,
>>
>> Thanks for your patch! However...
>>
>> Às 15:14 de 04/12/21, 6812skiii@gmail.com escreveu:
>>> From: Jangwoong Kim <6812skiii@gmail.com>
>>>
>>> We return 1, not the index of futex woken up.
>>>
>>> Signed-off-by: Jangwoong Kim <6812skiii@gmail.com>
>>> ---
>>>  kernel/futex/waitwake.c | 4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/kernel/futex/waitwake.c b/kernel/futex/waitwake.c
>>> index 4ce0923f1ce3..d148e5d4956b 100644
>>> --- a/kernel/futex/waitwake.c
>>> +++ b/kernel/futex/waitwake.c
>>> @@ -455,8 +455,8 @@ static int futex_wait_multiple_setup(struct futex_vector *vs, int count, int *wo
>>>
>>>               /*
>>>                * Even if something went wrong, if we find out that a futex
>>> -              * was woken, we don't return error and return this index to
>>> -              * userspace
>>> +              * was woken, we don't return error and make userspace aware
>>> +              * of this by returning 1.
>>
>> We return to userspace the value at *woken, so your fix is wrong. Have a
>> look at futex_wait_multiple():
>>
>>                 ret = futex_wait_multiple_setup(vs, count, &hint);
>>                 if (ret) {
>>                         if (ret > 0) {
>>                                 /* A futex was woken during setup */
>>                                 ret = hint;
>>                         }
>>                         return ret;
>>                 }
>>
>> When we return 1 at futex_wait_multiple_setup(), we end up returning the
>> hint/woken value to userspace.
>>
>> Let me know if you have questions.
>>
>>         André