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References: <20211204181458.10076-1-6812skiii@gmail.com> <f7d9194b-6681-48f0-b5e9-11f43d2849bd@collabora.com>
In-Reply-To: <f7d9194b-6681-48f0-b5e9-11f43d2849bd@collabora.com>
From:   Jangwoong Kim <6812skiii@gmail.com>
Date:   Tue, 7 Dec 2021 02:44:36 +0900
Message-ID: <CAF=mnpi65WtnK_mF1f8GfMEczS1ruj8q4YbA18R5KvWcpkxLxw@mail.gmail.com>
Subject: Re: [PATCH] futex: Fix a faulty comment.
To:     =?UTF-8?Q?Andr=C3=A9_Almeida?= <andrealmeid@collabora.com>
Cc:     peterz@infradead.org, mingo@redhat.com, tglx@linutronix.de,
        dvhart@infradead.org, dave@stgolabs.net,
        linux-kernel@vger.kernel.org
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Hi Andr=C3=A9.

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 fute=
x
-                * was woken, we don't return error and return this index t=
o
-                * userspace
+                * Even if something went wrong, if we find out that any fu=
tex
+                * was woken, we don't return error and return the last ind=
ex
+                * awoken to userspace
                 */
                *woken =3D unqueue_multiple(vs, i);
                if (*woken >=3D 0)

I sent the patch because I thought this was important enough to be correcte=
d.

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.

2021=EB=85=84 12=EC=9B=94 6=EC=9D=BC (=EC=9B=94) =EC=98=A4=ED=9B=84 9:12, A=
ndr=C3=A9 Almeida <andrealmeid@collabora.com>=EB=8B=98=EC=9D=B4 =EC=9E=91=
=EC=84=B1:
>
> Hi Jangwoong,
>
> Thanks for your patch! However...
>
> =C3=80s 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_v=
ector *vs, int count, int *wo
> >
> >               /*
> >                * Even if something went wrong, if we find out that a fu=
tex
> > -              * was woken, we don't return error and return this index=
 to
> > -              * userspace
> > +              * was woken, we don't return error and make userspace aw=
are
> > +              * 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 =3D futex_wait_multiple_setup(vs, count, &hint);
>                 if (ret) {
>                         if (ret > 0) {
>                                 /* A futex was woken during setup */
>                                 ret =3D 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.
>
>         Andr=C3=A9