[PATCH 14/24] drm/i915: Manually unwind after a failed request allocation

[Chris Wilson]

In the next patches, we want to move the work out of freeing the request
and into its retirement (so that we can free the request without
requiring the struct_mutex). This means that we cannot rely on
unreferencing the request to completely teardown the request any more
and so we need to manually unwind the failed allocation. In doing so, we
reorder the allocation in order to make the unwind simple (and ensure
that we don't try to unwind a partial request that may have modified
global state).

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_gem.c | 29 +++++++++++------------------
 1 file changed, 11 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 3a7f604f6b46..93028d33be33 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2764,15 +2764,6 @@ __i915_gem_request_alloc(struct intel_engine_cs *engine,
 	req->ctx  = ctx;
 	i915_gem_context_reference(req->ctx);
 
-	if (i915.enable_execlists)
-		ret = intel_logical_ring_alloc_request_extras(req);
-	else
-		ret = intel_ring_alloc_request_extras(req);
-	if (ret) {
-		i915_gem_context_unreference(req->ctx);
-		goto err;
-	}
-
 	/*
 	 * Reserve space in the ring buffer for all the commands required to
 	 * eventually emit this request. This is to guarantee that the
@@ -2782,19 +2773,21 @@ __i915_gem_request_alloc(struct intel_engine_cs *engine,
 	 */
 	req->reserved_space = MIN_SPACE_FOR_ADD_REQUEST;
 	ret = intel_ring_begin(req, 0);
-	if (ret) {
-		/*
-		 * At this point, the request is fully allocated even if not
-		 * fully prepared. Thus it can be cleaned up using the proper
-		 * free code.
-		 */
-		i915_gem_request_unreference(req);
-		return ret;
-	}
+	if (ret)
+		goto err_ctx;
+
+	if (i915.enable_execlists)
+		ret = intel_logical_ring_alloc_request_extras(req);
+	else
+		ret = intel_ring_alloc_request_extras(req);
+	if (ret)
+		goto err_ctx;
 
 	*req_out = req;
 	return 0;
 
+err_ctx:
+	i915_gem_context_unreference(ctx);
 err:
 	kmem_cache_free(dev_priv->requests, req);
 	return ret;
-- 
2.8.1