Date: Thu, 22 May 2014 22:23:43 +0400 From: Chagin Dmitry <dchagin@freebsd.org> To: Hans Petter Selasky <hps@selasky.org> Cc: freebsd-multimedia@FreeBSD.org, FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: Patch for Linux Futexes Message-ID: <20140522182343.GA2825@dchagin.static.corbina.net> In-Reply-To: <537DDA2E.6030609@selasky.org> References: <537DDA2E.6030609@selasky.org>
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On Thu, May 22, 2014 at 01:06:22PM +0200, Hans Petter Selasky wrote:
> Hi,
>
> When using the Linux Skype client under FreeBSD I sometimes see that the
> Audio disappears in the one direction. When I check "ps auxw" I see
> skype is stuck on a so-called Futex. I looked into the Linux futex code
> and see that wakeup_one() is used instead of wakeup(). Maybe others can
> test too and verify if replacing wakeup_one() by wakeup() makes any
> difference in for Linux applications using Futexes.
>
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
>
>
> > diff --git a/sys/compat/linux/linux_futex.c b/sys/compat/linux/linux_futex.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 |= 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 == n)
> > break;
> > }
> > @@ -525,7 +525,7 @@ futex_requeue(struct futex *f, int n, struct futex *f2, int n2)
> > wp->wp_flags |= 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);
>
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Have fun!
chd
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