On Thu, Jun 23, 2016 at 08:41:09PM +0200, Michael Kerrisk (man-pages) wrote:
> On 06/23/2016 08:28 PM, Darren Hart wrote:
> > On Thu, Jun 23, 2016 at 07:26:52PM +0200, Thomas Gleixner wrote:
> > > On Thu, 23 Jun 2016, Darren Hart wrote:
> > > > On Thu, Jun 23, 2016 at 03:40:36PM +0200, Thomas Gleixner wrote:
> > > > In my opinion, we should treat the timeout value as relative for
> > > > FUTEX_WAIT
> > > > regardless of the CLOCK used.
> > >
> > > Which requires even more changes as you have to select which clock you are
> > > using for adding the base time.
> >
> > Right, something like the following?
> >
> >
> > diff --git a/kernel/futex.c b/kernel/futex.c
> > index 33664f7..c39d807 100644
> > --- a/kernel/futex.c
> > +++ b/kernel/futex.c
> > @@ -3230,8 +3230,12 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op,
> > u32, val,
> > return -EINVAL;
> >
> > t = timespec_to_ktime(ts);
> > - if (cmd == FUTEX_WAIT)
> > - t = ktime_add_safe(ktime_get(), t);
> > + if (cmd == FUTEX_WAIT) {
> > + if (cmd & FUTEX_CLOCK_REALTIME)
> > + t = ktime_add_safe(ktime_get_real(), t);
> > + else
> > + t = ktime_add_safe(ktime_get(), t);
> > + }
> > tp = &t;
> > }
> > /*
>
> Just in the interests of readability/maintainability, might it not
> make some sense to recode the timeout handling for FUTEX_WAIT
> within futex_wait(). I think that part of the reason we're in this
> mess of inconsistency is that timeout interpretation is being handled
> at too many different points in the code.
I agree, that is indeed why I missed it in my original patch.
>
> > And as a follow-on, what is the reason for FUTEX_LOCK_PI only using
> > CLOCK_REALTIME? It seems reasonable to me that a user may want to wait a
> > specific amount of time, regardless of wall time.
>
> Yes, that's another weird inconsistency.
>
> Thanks,
>
> Michael
>
>
> --
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> Linux/UNIX System Programming Training: http://man7.org/training/
>
--
Darren Hart
Intel Open Source Technology Center
