On Mon, 13 Mar 2017, Peter Zijlstra wrote:
> On Tue, Mar 07, 2017 at 03:31:50PM +0100, Thomas Gleixner wrote:
> > On Sat, 4 Mar 2017, Peter Zijlstra wrote:
> >
> > > The problem with returning -EAGAIN when the waiter state mismatches is
> > > that it becomes very hard to proof a bounded execution time on the
> > > operation. And seeing that this is a RT operation, this is somewhat
> > > important.
> > >
> > > While in practise it will be very unlikely to ever really take more
> > > than one or two rounds, proving so becomes rather hard.
> >
> > Oh no. Assume the following:
> >
> > T1 and T2 are both pinned to CPU0. prio(T2) > prio(T1)
> >
> > CPU0
> >
> > T1
> > lock_pi()
> > queue_me() <- Waiter is visible
> >
> > preemption
> >
> > T2
> > unlock_pi()
> > loops with -EAGAIN forever
>
> So this is true before the last patch; but if we look at the locking
> changes brought by that (pasting its changelog here):
I was referring to the state before the last patch and your wording in the
changelog of this being very unlikely.
Thanks,
tglx
