From 08bec5b4edd13a7cb0bc2fb27c529d794ae67054 Mon Sep 17 00:00:00 2001 From: David Herrmann Date: Thu, 15 Nov 2012 13:04:37 +0000 Subject: [PATCH] drm: fix returning -EINVAL on setmaster if another master is active We link every DRM "file_priv" to a "drm_master" structure. Currently, the drmSetMaster() call returns 0 when there is _any_ active master associated with the "drm_master" structure of the calling "file_priv". This means, that after drmSetMaster() we are not guaranteed to be DRM-Master and might not be able to perform mode-setting. A way to reproduce this is by starting weston with the DRM backend from within an X-console (eg., xterm). Because the xserver's "drm_master" is currently active, weston is assigned to the same master but is inactive because its VT is inactive and the xserver is still active. But when "fake-activating" weston, it calls drmSetMaster(). With current behavior this returns "0/success" and weston thinks that it is DRM-Master, even though it is not (as the xserver is still DRM-Master). Expected behavior would be drmSetMaster() to return -EINVAL, because the xserver is still DRM-Master. This patch changes exactly that. The only way this bogus behavior would be useful is for clients to check whether their associated "drm_master" is currently the active DRM-Master. But this logic fails if no DRM-Master is currently active at all. Because then the client itself would become DRM-Master (if it is root) and this makes this whole thing useles. Also note that the second "if-condition": file_priv->minor->master != file_priv->master is always true and can be skipped. Signed-off-by: David Herrmann Signed-off-by: Dave Airlie --- drivers/gpu/drm/drm_stub.c | 24 ++++++++++++------------ 1 file changed, 12 insertions(+), 12 deletions(-) diff --git a/drivers/gpu/drm/drm_stub.c b/drivers/gpu/drm/drm_stub.c index c236fd27eba6..581e61d04057 100644 --- a/drivers/gpu/drm/drm_stub.c +++ b/drivers/gpu/drm/drm_stub.c @@ -221,20 +221,20 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data, if (!file_priv->master) return -EINVAL; - if (!file_priv->minor->master && - file_priv->minor->master != file_priv->master) { - mutex_lock(&dev->struct_mutex); - file_priv->minor->master = drm_master_get(file_priv->master); - file_priv->is_master = 1; - if (dev->driver->master_set) { - ret = dev->driver->master_set(dev, file_priv, false); - if (unlikely(ret != 0)) { - file_priv->is_master = 0; - drm_master_put(&file_priv->minor->master); - } + if (file_priv->minor->master) + return -EINVAL; + + mutex_lock(&dev->struct_mutex); + file_priv->minor->master = drm_master_get(file_priv->master); + file_priv->is_master = 1; + if (dev->driver->master_set) { + ret = dev->driver->master_set(dev, file_priv, false); + if (unlikely(ret != 0)) { + file_priv->is_master = 0; + drm_master_put(&file_priv->minor->master); } - mutex_unlock(&dev->struct_mutex); } + mutex_unlock(&dev->struct_mutex); return 0; } -- 2.20.1