[Mesa-dev] [PATCH] st/dri: Remove useless flush front.

[Jose Fonseca]

----- Original Message -----
> Where else would the flush go? 

Maybe one of the callers already invoked glFlush, or something like that.

> I'll look into fixing it differently
> but if the flush is anywhere in the makecurrent path, the same issue
> will happen. Again, none of the classic dri drivers do it.

If you wanna a short term fix, it might be OK with just commenting out the flush call, but please leave a note there saying that a flush is needed for strict conformance.

Jose

> Stéphane
> 
> 
> 2012/1/11 Jose Fonseca <jfonseca at vmware.com>:
> > Stephane,
> >
> > Although flushing the front buffer may be unnecessary, flushing
> > itself is not, as glXMakeCurrent mandates that the current must be
> > flushed:
> >
> >   "Pending commands to the previous context, if any, are flushed
> >   before it is released."
> >
> > So this flush call can only be removed, if a flush is done
> > elsewhere in DRI shared code, otherwise rendering queued in that
> > context may not happen.
> >
> > Jose
> >
> > ----- Original Message -----
> >> In the following scenario:
> >> - CreateContext C1
> >> - MakeCurrent C1
> >> - DestroyContext C1 (does not actually destroy the first context,
> >> postponed
> >>   until the next MakeCurrent)
> >> - CreateContext C2
> >> - MakeCurrent C2
> >>
> >> MakeCurrent will call flush on a context which might not even have
> >> had a front
> >> buffer, leading to crashes. Since none of the dri drivers use the
> >> flush in
> >> their unbind_context implementation either, we remove this useless
> >> flush front
> >> call.
> >>
> >> This fixes GPU crashes with Chrome and gallium drivers.
> >> ---
> >>  .../state_trackers/dri/common/dri_context.c        |    1 -
> >>  1 files changed, 0 insertions(+), 1 deletions(-)
> >>
> >> diff --git a/src/gallium/state_trackers/dri/common/dri_context.c
> >> b/src/gallium/state_trackers/dri/common/dri_context.c
> >> index b47d8d9..226c630 100644
> >> --- a/src/gallium/state_trackers/dri/common/dri_context.c
> >> +++ b/src/gallium/state_trackers/dri/common/dri_context.c
> >> @@ -188,7 +188,6 @@ dri_unbind_context(__DRIcontext * cPriv)
> >>
> >>     if (--ctx->bind_count == 0) {
> >>        if (ctx->st == ctx->stapi->get_current(ctx->stapi)) {
> >> -         ctx->st->flush(ctx->st, ST_FLUSH_FRONT, NULL);
> >>           stapi->make_current(stapi, NULL, NULL, NULL);
> >>        }
> >>     }
> >> --
> >> 1.7.5.3.367.ga9930
> >>
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> >>
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