drm/i915: Mark up potential allocation paths within i915_sw_fence as might_sleep

As kmalloc is allowed to block (if given the right flags), mark up the
two i915_sw_fence routines that may call kmalloc as potential sleeping
routines.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171212180652.22061-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_sw_fence.c

@@ -303,6 +303,7 @@ static int __i915_sw_fence_await_sw_fence(struct i915_sw_fence *fence,
 	int pending;
 
 	debug_fence_assert(fence);
+	might_sleep_if(gfpflags_allow_blocking(gfp));
 
 	if (i915_sw_fence_done(signaler))
 		return 0;
@@ -419,6 +420,7 @@ int i915_sw_fence_await_dma_fence(struct i915_sw_fence *fence,
 	int ret;
 
 	debug_fence_assert(fence);
+	might_sleep_if(gfpflags_allow_blocking(gfp));
 
 	if (dma_fence_is_signaled(dma))
 		return 0;
@@ -465,6 +467,7 @@ int i915_sw_fence_await_reservation(struct i915_sw_fence *fence,
 	int ret = 0, pending;
 
 	debug_fence_assert(fence);
+	might_sleep_if(gfpflags_allow_blocking(gfp));
 
 	if (write) {
 		struct dma_fence **shared;