[PATCH] drm/gem: Document that handle_create must be the last step

[PATCH] drm/gem: Document that handle_create must be the last step

[Daniel Vetter]

It published the gem object to userspace, by that point other threads
can guess the id and start using it. And gem IDs are _very_ easy to
guess (it's just an idr).

Since gem objects is the only thing we allow drivers to create
themselves (all the kms/prime/syncobj stuff is handled by the core) no
other functions seem to be in need of this clarification.

Motivated by reviewing the xen-front kms driver.

Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
---
 drivers/gpu/drm/drm_gem.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 4975ba9a7bc8..4a16d7b26c89 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -436,9 +436,12 @@ drm_gem_handle_create_tail(struct drm_file *file_priv,
  * @obj: object to register
  * @handlep: pionter to return the created handle to the caller
  *
- * Create a handle for this object. This adds a handle reference
- * to the object, which includes a regular reference count. Callers
- * will likely want to dereference the object afterwards.
+ * Create a handle for this object. This adds a handle reference to the object,
+ * which includes a regular reference count. Callers will likely want to
+ * dereference the object afterwards.
+ *
+ * Since this publishes @obj to userspace it must be fully set up by this point,
+ * drivers must call this last in their buffer object creation callbacks.
  */
 int drm_gem_handle_create(struct drm_file *file_priv,
 			  struct drm_gem_object *obj,
-- 
2.16.2

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Re: [PATCH] drm/gem: Document that handle_create must be the last step

[Oleksandr Andrushchenko]

On 03/22/2018 10:02 AM, Daniel Vetter wrote:
> It published
s/It/If
>   the gem object to userspace, by that point other threads
> can guess the id and start using it. And gem IDs are _very_ easy to
> guess (it's just an idr).
>
> Since gem objects is the only thing we allow drivers to create
> themselves (all the kms/prime/syncobj stuff is handled by the core) no
> other functions seem to be in need of this clarification.
>
> Motivated by reviewing the xen-front kms driver.
>
> Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>   drivers/gpu/drm/drm_gem.c | 9 ++++++---
>   1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index 4975ba9a7bc8..4a16d7b26c89 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -436,9 +436,12 @@ drm_gem_handle_create_tail(struct drm_file *file_priv,
>    * @obj: object to register
>    * @handlep: pionter to return the created handle to the caller
>    *
> - * Create a handle for this object. This adds a handle reference
> - * to the object, which includes a regular reference count. Callers
> - * will likely want to dereference the object afterwards.
> + * Create a handle for this object. This adds a handle reference to the object,
> + * which includes a regular reference count. Callers will likely want to
> + * dereference the object afterwards.
> + *
> + * Since this publishes @obj to userspace it must be fully set up by this point,
> + * drivers must call this last in their buffer object creation callbacks.
>    */
>   int drm_gem_handle_create(struct drm_file *file_priv,
>   			  struct drm_gem_object *obj,

Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

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Re: [PATCH] drm/gem: Document that handle_create must be the last step

[Daniel Vetter]

On Thu, Mar 22, 2018 at 10:12:03AM +0200, Oleksandr Andrushchenko wrote:
> On 03/22/2018 10:02 AM, Daniel Vetter wrote:
> > It published
> s/It/If

Doesn't make much sense to me, It = drm_gem_handle_create.

> >   the gem object to userspace, by that point other threads
> > can guess the id and start using it. And gem IDs are _very_ easy to
> > guess (it's just an idr).
> > 
> > Since gem objects is the only thing we allow drivers to create
> > themselves (all the kms/prime/syncobj stuff is handled by the core) no
> > other functions seem to be in need of this clarification.
> > 
> > Motivated by reviewing the xen-front kms driver.
> > 
> > Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > ---
> >   drivers/gpu/drm/drm_gem.c | 9 ++++++---
> >   1 file changed, 6 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> > index 4975ba9a7bc8..4a16d7b26c89 100644
> > --- a/drivers/gpu/drm/drm_gem.c
> > +++ b/drivers/gpu/drm/drm_gem.c
> > @@ -436,9 +436,12 @@ drm_gem_handle_create_tail(struct drm_file *file_priv,
> >    * @obj: object to register
> >    * @handlep: pionter to return the created handle to the caller
> >    *
> > - * Create a handle for this object. This adds a handle reference
> > - * to the object, which includes a regular reference count. Callers
> > - * will likely want to dereference the object afterwards.
> > + * Create a handle for this object. This adds a handle reference to the object,
> > + * which includes a regular reference count. Callers will likely want to
> > + * dereference the object afterwards.
> > + *
> > + * Since this publishes @obj to userspace it must be fully set up by this point,
> > + * drivers must call this last in their buffer object creation callbacks.
> >    */
> >   int drm_gem_handle_create(struct drm_file *file_priv,
> >   			  struct drm_gem_object *obj,
> 
> Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

Applied, thx for review.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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