drm/i915/execlists: Process interrupted context on reset

By stopping the rings, we may trigger an arbitration point resulting in
a premature context-switch (i.e. a completion event before the request
is actually complete). This clears the active context before the reset,
but we must remember to rewind the incomplete context for replay upon
resume.

Fixes: 1863e302 ("drm/i915/execlists: Always reset the context's RING registers")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190716124931.5870-3-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -1425,7 +1425,8 @@ static void process_csb(struct intel_engine_cs *engine)
 			 * coherent (visible from the CPU) before the
 			 * user interrupt and CSB is processed.
 			 */
-			GEM_BUG_ON(!i915_request_completed(*execlists->active));
+			GEM_BUG_ON(!i915_request_completed(*execlists->active) &&
+				   !reset_in_progress(execlists));
 			execlists_schedule_out(*execlists->active++);
 
 			GEM_BUG_ON(execlists->active - execlists->inflight >
@@ -2251,7 +2252,7 @@ static void __execlists_reset(struct intel_engine_cs *engine, bool stalled)
 	 */
 	rq = execlists_active(execlists);
 	if (!rq)
-		return;
+		goto unwind;
 
 	ce = rq->hw_context;
 	GEM_BUG_ON(i915_active_is_idle(&ce->active));
@@ -2328,6 +2329,7 @@ static void __execlists_reset(struct intel_engine_cs *engine, bool stalled)
 	intel_ring_update_space(ce->ring);
 	__execlists_update_reg_state(ce, engine);
 
+unwind:
 	/* Push back any incomplete requests for replay after the reset. */
 	__unwind_incomplete_requests(engine);
 }