On Mon, Oct 25, 2021 at 10:18 AM Richard Henderson <
richard.henderson@linaro.org> wrote:

> On 10/25/21 7:07 AM, Stefan Hajnoczi wrote:
> > This is a preview of how we can solve the coroutines TLS problem.
> Coroutines
> > re-entered from another thread sometimes see stale TLS values. This
> happens
> > because compilers may cache values across yield points, so a value from
> the
> > previous thread will be used when the coroutine is re-entered in another
> > thread.
>
> I'm not thrilled by this, but I guess it does work.
>
> It could be worthwhile to add some inline asm instead for specific hosts
> -- one
> instruction instead of an out-of-line call.
>
>
> > Serge Guelton developed this technique, see the first patch for details.
> I'm
> > submitting it for discussion before I go ahead with a full conversion of
> the
> > source tree.
> >
> > Todo:
> > - Convert all uses of __thread
> > - Extend checkpatch.pl to reject code that uses __thread
>
> Absolutely not.  *Perhaps* one or two tls variables which are accessible
> by coroutines,
> but there are plenty that have absolutely no relation.  Especially
> everything related to
> user-only execution.
>

I had the same worry. I'd also worry that the hoops that are jumped through
for
coroutines would somehow conflict with the low-level user-only execution
environment. I mean, it should be fine, but I know I'd be cranky if I traced
obscure regressions to being forced to use this construct...

Warner


> r~
>
>