Re: [PATCH 3/4] drm/gem: cleanup prime lock issue with drm_gem_handle_create_tail

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Oct 15, 2015 at 11:51:40AM +1000, Dave Airlie wrote:
> From: Dave Airlie <airlied@redhat.com>
> 
> This patch cleans up one locking order issue with a deadlock on
> the prime lock.
> 
> It avoids calling the prime delete function from drm_gem_handle_create_tail,
> and instead open codes the exit paths, it also splits the common code
> out for the exit path which can use it.
> 
> This means the callee has to call the prime cleanup paths, which is fine
> since this is only the prime code and it holds the lock already.
> 
> This is based on an patch/idea by Daniel Vetter, but I've cleaned it up
> and reworked it.
> 
> Signed-off-by: Dave Airlie <airlied@redhat.com>
> ---
>  drivers/gpu/drm/drm_gem.c   | 55 +++++++++++++++++++++++++++------------------
>  drivers/gpu/drm/drm_prime.c |  3 +++
>  2 files changed, 36 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index 12d0dc7..49354d7 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -239,14 +239,12 @@ drm_gem_object_handle_unreference_unlocked(struct drm_gem_object *obj)
>  	drm_gem_object_unreference_unlocked(obj);
>  }
>  
> +/* use for deletion and failure in allocation */
>  static void
> -drm_gem_handle_delete_tail(struct drm_file *filp,
> -			   struct drm_gem_object *obj)
> +drm_gem_handle_cleanup(struct drm_file *filp,
> +		       struct drm_gem_object *obj)
>  {
>  	struct drm_device *dev = obj->dev;
> -
> -	if (drm_core_check_feature(dev, DRIVER_PRIME))
> -		drm_gem_remove_prime_handles(obj, filp);
>  	drm_vma_node_revoke(&obj->vma_node, filp->filp);
>  
>  	if (dev->driver->gem_close_object)
> @@ -254,6 +252,17 @@ drm_gem_handle_delete_tail(struct drm_file *filp,
>  	drm_gem_object_handle_unreference_unlocked(obj);
>  }
>  
> +static void
> +drm_gem_handle_delete_tail_prime(struct drm_file *filp,
> +				 struct drm_gem_object *obj)
> +{
> +	struct drm_device *dev = obj->dev;
> +
> +	if (drm_core_check_feature(dev, DRIVER_PRIME))
> +		drm_gem_remove_prime_handles(obj, filp);
> +	drm_gem_handle_cleanup(filp, obj);
> +}
> +
>  /**
>   * drm_gem_handle_delete - deletes the given file-private handle
>   * @filp: drm file-private structure to use for the handle look up
> @@ -291,7 +300,7 @@ drm_gem_handle_delete(struct drm_file *filp, u32 handle)
>  	idr_remove(&filp->object_idr, handle);
>  	spin_unlock(&filp->table_lock);
>  
> -	drm_gem_handle_delete_tail(filp, obj);
> +	drm_gem_handle_delete_tail_prime(filp, obj);
>  	return 0;
>  }
>  EXPORT_SYMBOL(drm_gem_handle_delete);
> @@ -333,6 +342,17 @@ drm_gem_handle_create_tail(struct drm_file *file_priv,
>  
>  	WARN_ON(!mutex_is_locked(&dev->object_name_lock));
>  
> +	ret = drm_vma_node_allow(&obj->vma_node, file_priv->filp);
> +	if (ret) {
> +		goto out_unlock;
> +	}
> +
> +	if (dev->driver->gem_open_object) {
> +		ret = dev->driver->gem_open_object(obj, file_priv);
> +		if (ret)
> +			goto out_vma;
> +	}
> +
>  	/*
>  	 * Get the user-visible handle using idr.  Preload and perform
>  	 * allocation under our spinlock.
> @@ -347,26 +367,17 @@ drm_gem_handle_create_tail(struct drm_file *file_priv,
>  	idr_preload_end();
>  	mutex_unlock(&dev->object_name_lock);
>  	if (ret < 0) {
> -		drm_gem_object_handle_unreference_unlocked(obj);
> +		drm_gem_handle_cleanup(file_priv, obj);
>  		return ret;
>  	}
>  	*handlep = ret;
>  
> -	ret = drm_vma_node_allow(&obj->vma_node, file_priv->filp);
> -	if (ret) {
> -		drm_gem_handle_delete(file_priv, *handlep);
> -		return ret;
> -	}
> -
> -	if (dev->driver->gem_open_object) {
> -		ret = dev->driver->gem_open_object(obj, file_priv);
> -		if (ret) {
> -			drm_gem_handle_delete(file_priv, *handlep);
> -			return ret;
> -		}
> -	}
> -
>  	return 0;
> +out_vma:
> +	drm_vma_node_revoke(&obj->vma_node, file_priv->filp);
> +out_unlock:
> +	mutex_unlock(&dev->object_name_lock);
> +	return ret;
>  }
>  
>  /**
> @@ -717,7 +728,7 @@ drm_gem_object_release_handle(int id, void *ptr, void *data)
>  	struct drm_file *file_priv = data;
>  	struct drm_gem_object *obj = ptr;
>  
> -	drm_gem_handle_delete_tail(file_priv, obj);
> +	drm_gem_handle_delete_tail_prime(file_priv, obj);
>  	return 0;
>  }
>  
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index d22ce83..88c004e 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -590,6 +590,9 @@ int drm_gem_prime_fd_to_handle(struct drm_device *dev,
>  
>  	/* drm_gem_handle_create_tail unlocks dev->object_name_lock. */
>  	ret = drm_gem_handle_create_tail(file_priv, obj, handle);
> +	if (ret)
> +		drm_prime_remove_buf_handle_locked(&file_priv->prime,
> +						   obj->dma_buf);

Why is this needed? We haven't yet added the handle the buffer lookup
table at this point. the create_handle_tail changes look good, so with
this hunk here removed the patch is

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>  	drm_gem_object_unreference_unlocked(obj);
>  	if (ret)
>  		goto out_put;
> -- 
> 2.5.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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