drm/i915: don't hang userspace when the gpu reset is stuck

With the gpu reset no longer using a trylock we've increased the
chances of userspace getting stuck quite a bit. To make that
(hopefully) rare case more paletable time out when waiting for the gpu
reset code to complete and signal this little issue to the caller by
returning -EIO.

This should help userspace to somewhat gracefully fall back and
hopefully allow the user to grab some logs and reboot the machine
(instead of staring at a frozen X screen in agony).

Suggested by Chris Wilson because I've been stubborn about allowing
the gpu reset code no to fail, ever (by removing the trylock).
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -96,9 +96,18 @@ i915_gem_wait_for_error(struct drm_device *dev)
 	if (!atomic_read(&dev_priv->mm.wedged))
 		return 0;
 
-	ret = wait_for_completion_interruptible(x);
-	if (ret)
+	/*
+	 * Only wait 10 seconds for the gpu reset to complete to avoid hanging
+	 * userspace. If it takes that long something really bad is going on and
+	 * we should simply try to bail out and fail as gracefully as possible.
+	 */
+	ret = wait_for_completion_interruptible_timeout(x, 10*HZ);
+	if (ret == 0) {
+		DRM_ERROR("Timed out waiting for the gpu reset to complete\n");
+		return -EIO;
+	} else if (ret < 0) {
 		return ret;
+	}
 
 	if (atomic_read(&dev_priv->mm.wedged)) {
 		/* GPU is hung, bump the completion count to account for