[Outreachy kernel] [PATCH] drm/gem: use new idr deletion interface to cleanup drm_gem_handle_delete()

Tue Sep 26 10:20:18 UTC 2017

On Tue, 26 Sep 2017, Daniel Vetter wrote:

> On Tue, Sep 26, 2017 at 10:47 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
> > On Tue, Sep 26, 2017 at 10:38 AM, Julia Lawall <julia.lawall at lip6.fr> wrote:
> >>
> >>
> >> On Tue, 26 Sep 2017, Daniel Vetter wrote:
> >>
> >>> On Tue, Sep 26, 2017 at 12:17:28AM +0530, Aishwarya Pant wrote:
> >>> > The IDR deletion interface now returns the deleted entry or NULL if it was not
> >>> > present. So we don't have to do the extra work of checking if we have a
> >>> > reference on the drm_gem_object, this can be handled by checking the return
> >>> > value from idr_remove() and the extra locks can be dropped.
> >>> >
> >>> > Signed-off-by: Aishwarya Pant <aishpant at gmail.com>
> >>>
> >>> Haneen is already working on this task, with the patch just merged. Please
> >>> coordinate with mentors (me or Sean Paul) before starting on something to
> >>> avoid such clashes in the future.
> >>>
> >>> Note also that some todo items are just ideas, and need confirmation with
> >>> relevant maintainers first.
> >>
> >> Not sure where the mixup happened, but anyone who starts on a project
> >> specific task should note that on the outreachy kernel wiki and before
> >> starting on a project specific task one should check that no one is
> >> working on it.  If someone started some time ago, and the code doesn't
> >> seem to have changed, ask the person who claimed the task or the mentor.
> >
> > Hm, the dri-devel tasks aren't on the wiki, but in the kernel sources.
> > Where should we put the scratch-pad to avoid such conflicts in the
> > future? E.g. the IIO subsytems has it's task on the wiki, where this
> > works much better.
>
> Ok, I found it. Looks like a few signed up for stuff, but without
> chatting with us first, and ended up picking tasks that need some
> serious GPU expertise. I.e. maybe suitable for a full internship,
> definitely not as starter tasks. I'll send out mails.

Thanks.  Everyone, please discuss with the mentor before picking a task.

julia

> -Daniel
>
>
> > -Daniel
> >
> >>
> >> thanks,
> >>
> >> julia
> >>
> >>>
> >>> Thanks, Daniel
> >>> > ---
> >>> >  drivers/gpu/drm/drm_gem.c | 21 ++-------------------
> >>> >  1 file changed, 2 insertions(+), 19 deletions(-)
> >>> >
> >>> > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> >>> > index c55f338..f62757a 100644
> >>> > --- a/drivers/gpu/drm/drm_gem.c
> >>> > +++ b/drivers/gpu/drm/drm_gem.c
> >>> > @@ -282,29 +282,12 @@ drm_gem_handle_delete(struct drm_file *filp, u32 handle)
> >>> >  {
> >>> >     struct drm_gem_object *obj;
> >>> >
> >>> > -   /* This is gross. The idr system doesn't let us try a delete and
> >>> > -    * return an error code.  It just spews if you fail at deleting.
> >>> > -    * So, we have to grab a lock around finding the object and then
> >>> > -    * doing the delete on it and dropping the refcount, or the user
> >>> > -    * could race us to double-decrement the refcount and cause a
> >>> > -    * use-after-free later.  Given the frequency of our handle lookups,
> >>> > -    * we may want to use ida for number allocation and a hash table
> >>> > -    * for the pointers, anyway.
> >>> > -    */
> >>> >     spin_lock(&filp->table_lock);
> >>> > -
> >>> > -   /* Check if we currently have a reference on the object */
> >>> > -   obj = idr_replace(&filp->object_idr, NULL, handle);
> >>> > -   spin_unlock(&filp->table_lock);
> >>> > -   if (IS_ERR_OR_NULL(obj))
> >>> > +   obj = idr_remove(&filp->object_idr, handle);
> >>> > +   if (!obj)
> >>> >             return -EINVAL;
> >>> > -
> >>> >     /* Release driver's reference and decrement refcount. */
> >>> >     drm_gem_object_release_handle(handle, obj, filp);
> >>> > -
> >>> > -   /* And finally make the handle available for future allocations. */
> >>> > -   spin_lock(&filp->table_lock);
> >>> > -   idr_remove(&filp->object_idr, handle);
> >>> >     spin_unlock(&filp->table_lock);
> >>> >
> >>> >     return 0;
> >>> > --
> >>> > 2.7.4
> >>> >
> >>> > --
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> >>>
> >>> --
> >>> Daniel Vetter
> >>> Software Engineer, Intel Corporation
> >>> http://blog.ffwll.ch
> >>>
> >>> --
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> >>>
> >
> >
> >
> > --
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > +41 (0) 79 365 57 48 - http://blog.ffwll.ch
>
>
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
>
> --
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