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 <dh.herrmann@googlemail.com> Signed-off-by: Dave Airlie <airlied@redhat.com>
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@ -221,20 +221,20 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data,
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if (!file_priv->master)
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return -EINVAL;
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if (!file_priv->minor->master &&
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file_priv->minor->master != file_priv->master) {
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mutex_lock(&dev->struct_mutex);
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file_priv->minor->master = drm_master_get(file_priv->master);
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file_priv->is_master = 1;
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if (dev->driver->master_set) {
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ret = dev->driver->master_set(dev, file_priv, false);
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if (unlikely(ret != 0)) {
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file_priv->is_master = 0;
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drm_master_put(&file_priv->minor->master);
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}
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if (file_priv->minor->master)
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return -EINVAL;
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mutex_lock(&dev->struct_mutex);
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file_priv->minor->master = drm_master_get(file_priv->master);
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file_priv->is_master = 1;
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if (dev->driver->master_set) {
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ret = dev->driver->master_set(dev, file_priv, false);
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if (unlikely(ret != 0)) {
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file_priv->is_master = 0;
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drm_master_put(&file_priv->minor->master);
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}
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mutex_unlock(&dev->struct_mutex);
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}
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mutex_unlock(&dev->struct_mutex);
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return 0;
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}
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