[Intel-gfx] [RFC 1/8] drm/i915: Downgrade tasklet GEM_BUG_ON for request not completed

[Chris Wilson]

Quoting jeff.mcgee at intel.com (2018-03-16 18:30:58)
> From: Jeff McGee <jeff.mcgee at intel.com>
> 
> It is possible for the hardware to be reset just as a context is
> completing. The reset post-processing may see the seqno update and
> assume that the context escaped corruption, but the context may
> have been disrupted in the save out process. The corruption may
> screw up the HEAD and TAIL pointers such that the next submission
> of the context switches out without running the intended request.
> The GEM_BUG_ON will be hit in this situation, but it is not really
> a driver error. So make it a GEM_WARN_ON so that we notice while
> letting hangcheck detect and clean up.
> 
> This patch is required to support the force preemption feature.
> 
> Test: Run IGT gem_exec_fpreempt repeatedly with
>       CONFIG_DRM_I915_DEBUG_GEM.
> Change-Id: I87da4b16bad805fe48153a9ed9169900681ebba7
> Signed-off-by: Jeff McGee <jeff.mcgee at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_lrc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index b44861459d24..7d93fcd56d34 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -920,7 +920,7 @@ static void intel_lrc_irq_handler(unsigned long data)
>                         GEM_BUG_ON(count == 0);
>                         if (--count == 0) {
>                                 GEM_BUG_ON(status & GEN8_CTX_STATUS_PREEMPTED);
> -                               GEM_BUG_ON(!i915_gem_request_completed(rq));
> +                               GEM_WARN_ON(!i915_gem_request_completed(rq));

Nope, either way you broke pretty badly.
-Chris