Messages in this thread | | | Subject | Re: futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op | From | "Michael Kerrisk (man-pages)" <> | Date | Thu, 23 Jun 2016 20:41:09 +0200 |
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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.
> 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/
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