drm/syncobj: Don't leak fences when WAIT_FOR_SUBMIT is set

commit 337fe9f5 upstream.

We attempt to get fences earlier in the hopes that everything will
already have fences and no callbacks will be needed.  If we do succeed
in getting a fence, getting one a second time will result in a duplicate
ref with no unref.  This is causing memory leaks in Vulkan applications
that create a lot of fences; playing for a few hours can, apparently,
bring down the system.

Cc: stable@vger.kernel.org
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107899Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180926071703.15257-1-jason.ekstrand@intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpu/drm/drm_syncobj.c

@@ -96,6 +96,8 @@ static int drm_syncobj_fence_get_or_add_callback(struct drm_syncobj *syncobj,
 {
 	int ret;
 
+	WARN_ON(*fence);
+
 	*fence = drm_syncobj_fence_get(syncobj);
 	if (*fence)
 		return 1;
@@ -656,6 +658,9 @@ static signed long drm_syncobj_array_wait_timeout(struct drm_syncobj **syncobjs,
 
 	if (flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT) {
 		for (i = 0; i < count; ++i) {
+			if (entries[i].fence)
+				continue;
+
 			drm_syncobj_fence_get_or_add_callback(syncobjs[i],
 							      &entries[i].fence,
 							      &entries[i].syncobj_cb,