drm/i915/selftests: Report ENOMEM clearly for an allocation failure

If we can not run the drunk_hole test because we couldn't allocate the
memory for the permutation array (even after we tried trimming the
size), report a clear ENOMEM. Similary, if we are asked to operate on a
hole too small for ourselves, make it skip quietly.

v2: Avoid malloc(0) since that returns ZERO_SIZE_PTR not NULL.
v3: Fixup similar construction for lowlevel_hole
v4: Use u64 >> 1 to avoid 64b div.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171117101732.4335-1-chris@chris-wilson.co.uk
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171117162945.16390-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/selftests/i915_gem_gtt.c

@@ -216,13 +216,21 @@ static int lowlevel_hole(struct drm_i915_private *i915,
 		hole_size = (hole_end - hole_start) >> size;
 		if (hole_size > KMALLOC_MAX_SIZE / sizeof(u32))
 			hole_size = KMALLOC_MAX_SIZE / sizeof(u32);
-		count = hole_size;
+		count = hole_size >> 1;
+		if (!count) {
+			pr_debug("%s: hole is too small [%llx - %llx] >> %d: %lld\n",
+				 __func__, hole_start, hole_end, size, hole_size);
+			break;
+		}
+
 		do {
-			count >>= 1;
 			order = i915_random_order(count, &prng);
-		} while (!order && count);
-		if (!order)
-			break;
+			if (order)
+				break;
+		} while (count >>= 1);
+		if (!count)
+			return -ENOMEM;
+		GEM_BUG_ON(!order);
 
 		GEM_BUG_ON(count * BIT_ULL(size) > vm->total);
 		GEM_BUG_ON(hole_start + count * BIT_ULL(size) > hole_end);
@@ -704,13 +712,21 @@ static int drunk_hole(struct drm_i915_private *i915,
 		hole_size = (hole_end - hole_start) >> size;
 		if (hole_size > KMALLOC_MAX_SIZE / sizeof(u32))
 			hole_size = KMALLOC_MAX_SIZE / sizeof(u32);
-		count = hole_size;
+		count = hole_size >> 1;
+		if (!count) {
+			pr_debug("%s: hole is too small [%llx - %llx] >> %d: %lld\n",
+				 __func__, hole_start, hole_end, size, hole_size);
+			break;
+		}
+
 		do {
-			count >>= 1;
 			order = i915_random_order(count, &prng);
-		} while (!order && count);
-		if (!order)
-			break;
+			if (order)
+				break;
+		} while (count >>= 1);
+		if (!count)
+			return -ENOMEM;
+		GEM_BUG_ON(!order);
 
 		/* Ignore allocation failures (i.e. don't report them as
 		 * a test failure) as we are purposefully allocating very