[Mesa-stable] [PATCH 5/6] i965: Avoid problems from referencing orphaned BOs after growing.

[Kenneth Graunke]

On Tuesday, November 28, 2017 4:13:20 PM PST Kenneth Graunke wrote:
> Growing the batch/state buffer is a lot more dangerous than I thought.
> 
> A number of places emit multiple state buffer sections, and then write
> data to the returned pointer, or save a pointer to brw->batch.state.bo
> and then use it in relocations.  If each call can grow, this can result
> in stale map references or stale BO pointers.  Furthermore, fences refer
> to the old batch BO, and that reference needs to continue working.
> 
> To avoid these woes, we avoid ever swapping the brw->batch.*.bo pointer,
> instead exchanging the brw_bo structures in place.  That way, stale BO
> references are fine - the GEM handle changes, but the brw_bo pointer
> doesn't.  We also defer the memcpy until a quiescent point, so callers
> can write to the returned pointer - which may be in either BO - and
> we'll sort it out and combine the two properly in the end.
> 
> Fixes GPU hangs in DiRT Rally.

Jordan and I retested, and it apparently does not fix those hangs.

I'm not sure what happened, but this series doesn't appear to help.
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