On Tue, Sep 26, 2017 at 10:20:47AM +0200, 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@xxxxxxxxx>
>
> 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.
Apologies for the mix-up, I'll make sure to check in with the mentors before
starting a task.
I looked over the other patch sent by Haneen today, there is one thing that I
could use some clarity on. I'm not sure how the -this is gross- comment is
obsolete since we can drop the check to idr_replace() and use the return value
from idr_remove() which seems neater in my opinion.
>
> Note also that some todo items are just ideas, and need confirmation with
> relevant maintainers first.
>
> 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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