Re: Patch for Linux Futexes

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On Thu, May 22, 2014 at 01:06:22PM +0200, Hans Petter Selasky wrote:
> Hi,
>=20
> When using the Linux Skype client under FreeBSD I sometimes see that the=
=20
> Audio disappears in the one direction. When I check "ps auxw" I see=20
> skype is stuck on a so-called Futex. I looked into the Linux futex code=
=20
> and see that wakeup_one() is used instead of wakeup(). Maybe others can=
=20
> test too and verify if replacing wakeup_one() by wakeup() makes any=20
> difference in for Linux applications using Futexes.
>=20

generally speaking the patch is not correct as futex_wake() should
wakeup n waiters which is specified by user space. and i think that
futex_wake() is correct.
so we must take a close look at futex_requeue() and FUTEX_WAKE_OP.

> --HPS
>=20
>=20
> > diff --git a/sys/compat/linux/linux_futex.c b/sys/compat/linux/linux_fu=
tex.c
> > index 9b4c92f..e893bf4 100644
> > --- a/sys/compat/linux/linux_futex.c
> > +++ b/sys/compat/linux/linux_futex.c
> > @@ -498,7 +498,7 @@ futex_wake(struct futex *f, int n, uint32_t bitset)
> >  		wp->wp_flags |=3D FUTEX_WP_REMOVED;
> >  		TAILQ_REMOVE(&f->f_waiting_proc, wp, wp_list);
> >  		LIN_SDT_PROBE1(futex, futex_wake, wakeup, wp);
> > -		wakeup_one(wp);
> > +		wakeup(wp);
> >  		if (++count =3D=3D n)
> >  			break;
> >  	}
> > @@ -525,7 +525,7 @@ futex_requeue(struct futex *f, int n, struct futex =
*f2, int n2)
> >  			wp->wp_flags |=3D FUTEX_WP_REMOVED;
> >  			TAILQ_REMOVE(&f->f_waiting_proc, wp, wp_list);
> >  			LIN_SDT_PROBE1(futex, futex_requeue, wakeup, wp);
> > -			wakeup_one(wp);
> > +			wakeup(wp);
> >  		} else {
> >  			LIN_SDT_PROBE3(futex, futex_requeue, requeue,
> >  			    f->f_uaddr, wp, f2->f_uaddr);
>=20
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--=20
Have fun!
chd

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