drm/i915: Allow fence allocations to fail

If a fence allocation fails in a blocking context, we will sleep on the
fence as a last resort. We can therefore allow ourselves to fail and
sleep on the fence instead of triggering a system-wide oom. This allows
us to throttle malicious clients that are consuming lots of system
resources by capping the amount of memory used by fences.

Testcase: igt/gem_shrink/execbufX
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171212180652.22061-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_clflush.c

@@ -167,7 +167,7 @@ bool i915_gem_clflush_object(struct drm_i915_gem_object *obj,
 		i915_sw_fence_await_reservation(&clflush->wait,
 						obj->resv, NULL,
 						true, I915_FENCE_TIMEOUT,
-						GFP_KERNEL);
+						I915_FENCE_GFP);
 
 		reservation_object_lock(obj->resv, NULL);
 		reservation_object_add_excl_fence(obj->resv, &clflush->dma);

drivers/gpu/drm/i915/i915_gem_context.c

@@ -617,7 +617,7 @@ int i915_gem_switch_to_kernel_context(struct drm_i915_private *dev_priv)
 			if (prev)
 				i915_sw_fence_await_sw_fence_gfp(&req->submit,
 								 &prev->submit,
-								 GFP_KERNEL);
+								 I915_FENCE_GFP);
 		}
 
 		/*

drivers/gpu/drm/i915/i915_gem_request.c

@@ -782,7 +782,7 @@ i915_gem_request_await_request(struct drm_i915_gem_request *to,
 	if (to->engine == from->engine) {
 		ret = i915_sw_fence_await_sw_fence_gfp(&to->submit,
 						       &from->submit,
-						       GFP_KERNEL);
+						       I915_FENCE_GFP);
 		return ret < 0 ? ret : 0;
 	}
 
@@ -810,7 +810,7 @@ i915_gem_request_await_request(struct drm_i915_gem_request *to,
 await_dma_fence:
 	ret = i915_sw_fence_await_dma_fence(&to->submit,
 					    &from->fence, 0,
-					    GFP_KERNEL);
+					    I915_FENCE_GFP);
 	return ret < 0 ? ret : 0;
 }
 
@@ -861,7 +861,7 @@ i915_gem_request_await_dma_fence(struct drm_i915_gem_request *req,
 		else
 			ret = i915_sw_fence_await_dma_fence(&req->submit, fence,
 							    I915_FENCE_TIMEOUT,
-							    GFP_KERNEL);
+							    I915_FENCE_GFP);
 		if (ret < 0)
 			return ret;
 

drivers/gpu/drm/i915/i915_gem_request.h

@@ -204,6 +204,8 @@ struct drm_i915_gem_request {
 	struct list_head client_link;
 };
 
+#define I915_FENCE_GFP (GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN)
+
 extern const struct dma_fence_ops i915_fence_ops;
 
 static inline bool dma_fence_is_i915(const struct dma_fence *fence)