Re: [PATCH v2] drm/gem: Fix GEM handle release errors

[Christian König]

Am 03.08.22 um 10:32 schrieb Jeffy Chen:
> Currently we are assuming a one to one mapping between dmabuf and handle
> when releasing GEM handles.
>
> But that is not always true, since we would create extra handles for the
> GEM obj in cases like gem_open() and getfb{,2}().
>
> A similar issue was reported at:
> https://lore.kernel.org/all/20211105083308.392156-1-jay.xu@xxxxxxxxxxxxxx/
>
> Another problem is that the drm_gem_remove_prime_handles() now only
> remove handle to the exported dmabuf (gem_obj->dma_buf), so the imported
> ones would leak:
> WARNING: CPU: 2 PID: 236 at drivers/gpu/drm/drm_prime.c:228 drm_prime_destroy_file_private+0x18/0x24
>
> Let's fix these by using handle to find the exact map to remove.

Well we are clearly something missing here. As far as I can see the 
current code is correct.

Creating multiple GEM handles for the same DMA-buf is possible, but illegal.

In other words when a GEM handle is exported as DMA-buf and imported 
again you should intentionally always get the same handle.

So this is pretty much a clear NAK to this patch since it shouldn't be 
necessary or something is seriously broken somewhere else.

Regards,
Christian.

> Signed-off-by: Jeffy Chen <jeffy.chen@xxxxxxxxxxxxxx>
> ---
>
> Changes in v2:
> Fix a typo of rbtree.
>
>   drivers/gpu/drm/drm_gem.c      | 17 +----------------
>   drivers/gpu/drm/drm_internal.h |  4 ++--
>   drivers/gpu/drm/drm_prime.c    | 20 ++++++++++++--------
>   3 files changed, 15 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index eb0c2d041f13..ed39da383570 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -168,21 +168,6 @@ void drm_gem_private_object_init(struct drm_device *dev,
>   }
>   EXPORT_SYMBOL(drm_gem_private_object_init);
>   
> -static void
> -drm_gem_remove_prime_handles(struct drm_gem_object *obj, struct drm_file *filp)
> -{
> -	/*
> -	 * Note: obj->dma_buf can't disappear as long as we still hold a
> -	 * handle reference in obj->handle_count.
> -	 */
> -	mutex_lock(&filp->prime.lock);
> -	if (obj->dma_buf) {
> -		drm_prime_remove_buf_handle_locked(&filp->prime,
> -						   obj->dma_buf);
> -	}
> -	mutex_unlock(&filp->prime.lock);
> -}
> -
>   /**
>    * drm_gem_object_handle_free - release resources bound to userspace handles
>    * @obj: GEM object to clean up.
> @@ -253,7 +238,7 @@ drm_gem_object_release_handle(int id, void *ptr, void *data)
>   	if (obj->funcs->close)
>   		obj->funcs->close(obj, file_priv);
>   
> -	drm_gem_remove_prime_handles(obj, file_priv);
> +	drm_prime_remove_buf_handle(&file_priv->prime, id);
>   	drm_vma_node_revoke(&obj->vma_node, file_priv);
>   
>   	drm_gem_object_handle_put_unlocked(obj);
> diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
> index 1fbbc19f1ac0..7bb98e6a446d 100644
> --- a/drivers/gpu/drm/drm_internal.h
> +++ b/drivers/gpu/drm/drm_internal.h
> @@ -74,8 +74,8 @@ int drm_prime_fd_to_handle_ioctl(struct drm_device *dev, void *data,
>   
>   void drm_prime_init_file_private(struct drm_prime_file_private *prime_fpriv);
>   void drm_prime_destroy_file_private(struct drm_prime_file_private *prime_fpriv);
> -void drm_prime_remove_buf_handle_locked(struct drm_prime_file_private *prime_fpriv,
> -					struct dma_buf *dma_buf);
> +void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv,
> +				 uint32_t handle);
>   
>   /* drm_drv.c */
>   struct drm_minor *drm_minor_acquire(unsigned int minor_id);
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index e3f09f18110c..bd5366b16381 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -190,29 +190,33 @@ static int drm_prime_lookup_buf_handle(struct drm_prime_file_private *prime_fpri
>   	return -ENOENT;
>   }
>   
> -void drm_prime_remove_buf_handle_locked(struct drm_prime_file_private *prime_fpriv,
> -					struct dma_buf *dma_buf)
> +void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv,
> +				 uint32_t handle)
>   {
>   	struct rb_node *rb;
>   
> -	rb = prime_fpriv->dmabufs.rb_node;
> +	mutex_lock(&prime_fpriv->lock);
> +
> +	rb = prime_fpriv->handles.rb_node;
>   	while (rb) {
>   		struct drm_prime_member *member;
>   
> -		member = rb_entry(rb, struct drm_prime_member, dmabuf_rb);
> -		if (member->dma_buf == dma_buf) {
> +		member = rb_entry(rb, struct drm_prime_member, handle_rb);
> +		if (member->handle == handle) {
>   			rb_erase(&member->handle_rb, &prime_fpriv->handles);
>   			rb_erase(&member->dmabuf_rb, &prime_fpriv->dmabufs);
>   
> -			dma_buf_put(dma_buf);
> +			dma_buf_put(member->dma_buf);
>   			kfree(member);
> -			return;
> -		} else if (member->dma_buf < dma_buf) {
> +			break;
> +		} else if (member->handle < handle) {
>   			rb = rb->rb_right;
>   		} else {
>   			rb = rb->rb_left;
>   		}
>   	}
> +
> +	mutex_unlock(&prime_fpriv->lock);
>   }
>   
>   void drm_prime_init_file_private(struct drm_prime_file_private *prime_fpriv)