在 2018-07-11三的 17:56 +0200，Noralf Trønnes写道：
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.
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
Tested on sun4i-drm: ``` [ 1.361768] sun4i-drm display-engine: bound 1100000.mixer (ops 0xc0ccf608) [ 1.369008] sun4i-drm display-engine: bound 1c0c000.lcd-controller (ops 0xc0ccc8d8) [ 1.377644] sun8i-dw-hdmi 1ee0000.hdmi: Detected HDMI TX controller v1.32a with HDCP (sun8i_dw_hdmi_phy) [ 1.387637] sun8i-dw-hdmi 1ee0000.hdmi: registered DesignWare HDMI I2C bus driver [ 1.395527] sun4i-drm display-engine: bound 1ee0000.hdmi (ops 0xc0ccf08c) [ 1.402361] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013). [ 1.408987] [drm] No driver support for vblank timestamp query. [ 1.714324] Console: switching to colour frame buffer device 128x48 [ 1.736736] sun4i-drm display-engine: fb0: DRM emulated frame buffer device [ 1.744252] [drm] Initialized sun4i-drm 1.0.0 20150629 for display- engine on minor 0 ```
Tested-by: Icenowy Zheng icenowy@aosc.io
Thanks! Icenowy
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);