On Wed, Jul 11, 2018 at 05:56:32PM +0200, Noralf Trønnes wrote:
Commit 894a677f4b3e ("drm/cma-helper: Use the generic fbdev emulation") broke almost all drivers that use the CMA helper.
The reason is that drm_client_new() requires that the DRM device has been registered, but the drivers register fbdev before registering DRM.
Remove the requirement that DRM should be registered when creating a new client.
This creates a theoretical race condition where drm_client_new() races with drm_dev_unregister() resulting in the .unregister hook not being called.
Case: User loads module which calls drm_client_new(). Device is unplugged and drm_dev_unregister() is called.
If drm_dev_unregister() gets the clientlist_mutex first, the new client will never get it's unregister hook called.
As long as we assume that drm_client_new() is serialized against drm_dev_unregister (which it has to, or all the current fbdev code would be busted) I'm not seeing a race here.
We can't allow drm_client_new concurrently with drm_dev_register, but that feature got canned. So looks all good to me, and no races anywhere to be seen. Assuming you agree and update the commit message:
Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
Fixes: c76f0f7cb546 ("drm: Begin an API for in-kernel clients") Cc: Maxime Ripard maxime.ripard@bootlin.com Cc: Icenowy Zheng icenowy@aosc.io Cc: Chen-Yu Tsai wens@csie.org Cc: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Noralf Trønnes noralf@tronnes.org
drivers/gpu/drm/drm_client.c | 11 +---------- 1 file changed, 1 insertion(+), 10 deletions(-)
diff --git a/drivers/gpu/drm/drm_client.c b/drivers/gpu/drm/drm_client.c index 4039a4d103a8..9b142f58d489 100644 --- a/drivers/gpu/drm/drm_client.c +++ b/drivers/gpu/drm/drm_client.c @@ -78,7 +78,6 @@ EXPORT_SYMBOL(drm_client_close); int drm_client_new(struct drm_device *dev, struct drm_client_dev *client, const char *name, const struct drm_client_funcs *funcs) {
bool registered; int ret;
if (!drm_core_check_feature(dev, DRIVER_MODESET) ||
@@ -97,21 +96,13 @@ int drm_client_new(struct drm_device *dev, struct drm_client_dev *client, goto err_put_module;
mutex_lock(&dev->clientlist_mutex);
- registered = dev->registered;
- if (registered)
list_add(&client->list, &dev->clientlist);
- list_add(&client->list, &dev->clientlist); mutex_unlock(&dev->clientlist_mutex);
if (!registered) {
ret = -ENODEV;goto err_close;}
drm_dev_get(dev);
return 0;
-err_close:
- drm_client_close(client);
err_put_module: if (funcs) module_put(funcs->owner); -- 2.15.1