Re: [RFC PATCH 0/3] restartable sequences v2: fast user-space percpu critical sections

Peter Zijlstra
2016-04-07T15:39:55Z

On Thu, Apr 07, 2016 at 05:24:32PM +0200, Peter Zijlstra wrote:
> On Thu, Apr 07, 2016 at 07:35:26AM -0700, Andy Lutomirski wrote:
> > That way we could take an async signal, handle it, and resume, even in
> > the middle of a commit, without aborting. Of course, if the signal
> > hander tried to access the same rseq-protected resource, it would bump
> > the event counter and cause an abort.
>
> Ah, so what happens if the signal happens before the commit but after
> the load of the seqcount?
>
> Then, even if the signal motifies the count, we'll not observe.

Ah, and the same is true for preemptions. Which is why all this was
preemption driven, and not migration driven.