[PATCH] drm: Fixup hang when unregistering drm dev with open_count 0

[PATCH] drm: Fixup hang when unregistering drm dev with open_count 0

[Jeffy Chen]

My previous patch (c5d8fac2bf  drm: Unplug drm device when unregistering
it) calls drm_unplug_dev when unregistering drm dev. But if open_count
is 0, the unplug will try to unregister the drm dev again and cause
deadlock.

Fix it by dropping drm_unplug_dev and use drm_device_set_plug_state
directly.

Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>

---

 drivers/gpu/drm/drm_drv.c | 15 +--------------
 include/drm/drm_drv.h     |  1 -
 2 files changed, 1 insertion(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index ad13e20..cc2d018 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -355,19 +355,6 @@ void drm_put_dev(struct drm_device *dev)
 }
 EXPORT_SYMBOL(drm_put_dev);
 
-void drm_unplug_dev(struct drm_device *dev)
-{
-	mutex_lock(&drm_global_mutex);
-
-	drm_device_set_plug_state(dev, false);
-
-	if (dev->open_count == 0) {
-		drm_put_dev(dev);
-	}
-	mutex_unlock(&drm_global_mutex);
-}
-EXPORT_SYMBOL(drm_unplug_dev);
-
 /*
  * DRM internal mount
  * We want to be able to allocate our own "struct address_space" to control
@@ -825,7 +812,7 @@ void drm_dev_unregister(struct drm_device *dev)
 	drm_lastclose(dev);
 
 	dev->registered = false;
-	drm_unplug_dev(dev);
+	drm_device_set_plug_state(dev, false);
 
 	if (drm_core_check_feature(dev, DRIVER_MODESET))
 		drm_modeset_unregister_all(dev);
diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
index 0fefc3f..eb63078 100644
--- a/include/drm/drm_drv.h
+++ b/include/drm/drm_drv.h
@@ -544,7 +544,6 @@ void drm_dev_unregister(struct drm_device *dev);
 void drm_dev_ref(struct drm_device *dev);
 void drm_dev_unref(struct drm_device *dev);
 void drm_put_dev(struct drm_device *dev);
-void drm_unplug_dev(struct drm_device *dev);
 
 int drm_dev_set_unique(struct drm_device *dev, const char *name);
 
-- 
2.1.4

Re: [PATCH] drm: Fixup hang when unregistering drm dev with open_count 0

[Sean Paul]

On Wed, Apr 12, 2017 at 04:57:54AM +0800, Jeffy Chen wrote:
> My previous patch (c5d8fac2bf  drm: Unplug drm device when unregistering
> it) calls drm_unplug_dev when unregistering drm dev. But if open_count
> is 0, the unplug will try to unregister the drm dev again and cause
> deadlock.
> 
> Fix it by dropping drm_unplug_dev and use drm_device_set_plug_state
> directly.

Hi Jeffy,
That patch was not applied anywhere, the test robot just picked it up from the
mailing list.

Please squash this into the original patch and re-send.

Thanks,

Sean

> 
> Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
> 
> ---
> 
>  drivers/gpu/drm/drm_drv.c | 15 +--------------
>  include/drm/drm_drv.h     |  1 -
>  2 files changed, 1 insertion(+), 15 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index ad13e20..cc2d018 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -355,19 +355,6 @@ void drm_put_dev(struct drm_device *dev)
>  }
>  EXPORT_SYMBOL(drm_put_dev);
>  
> -void drm_unplug_dev(struct drm_device *dev)
> -{
> -	mutex_lock(&drm_global_mutex);
> -
> -	drm_device_set_plug_state(dev, false);
> -
> -	if (dev->open_count == 0) {
> -		drm_put_dev(dev);
> -	}
> -	mutex_unlock(&drm_global_mutex);
> -}
> -EXPORT_SYMBOL(drm_unplug_dev);
> -
>  /*
>   * DRM internal mount
>   * We want to be able to allocate our own "struct address_space" to control
> @@ -825,7 +812,7 @@ void drm_dev_unregister(struct drm_device *dev)
>  	drm_lastclose(dev);
>  
>  	dev->registered = false;
> -	drm_unplug_dev(dev);
> +	drm_device_set_plug_state(dev, false);
>  
>  	if (drm_core_check_feature(dev, DRIVER_MODESET))
>  		drm_modeset_unregister_all(dev);
> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
> index 0fefc3f..eb63078 100644
> --- a/include/drm/drm_drv.h
> +++ b/include/drm/drm_drv.h
> @@ -544,7 +544,6 @@ void drm_dev_unregister(struct drm_device *dev);
>  void drm_dev_ref(struct drm_device *dev);
>  void drm_dev_unref(struct drm_device *dev);
>  void drm_put_dev(struct drm_device *dev);
> -void drm_unplug_dev(struct drm_device *dev);
>  
>  int drm_dev_set_unique(struct drm_device *dev, const char *name);
>  
> -- 
> 2.1.4
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS