Re: [Intel-xe] [PATCH 4/5] drm/xe: Combine destroy_cb and destroy_work in xe_vma into union

[Matthew Brost <matthew.brost@intel.com>]

On Thu, Jul 13, 2023 at 04:23:43PM -0400, Rodrigo Vivi wrote:
> On Tue, Jul 11, 2023 at 02:27:47PM -0700, Matthew Brost wrote:
> > The callback kicks the worker thus mutually exclusive execution,
> > combining saves a bit of space in xe_vma.
> 
> could you please open up a bit on why they are multually exclusive?!
> 

Not sure how else to word this. The callback function (below) queues the
worker, the callback argument at this point is safe to clobber.

1047 static void vma_destroy_cb(struct dma_fence *fence,
1048                            struct dma_fence_cb *cb)
1049 {
1050         struct xe_vma *vma = container_of(cb, struct xe_vma, destroy_cb);
1051
1052         INIT_WORK(&vma->destroy_work, vma_destroy_work_func);
1053         queue_work(system_unbound_wq, &vma->destroy_work);
1054 }

Matt

> > 
> > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > ---
> >  drivers/gpu/drm/xe/xe_vm_types.h | 11 ++++++-----
> >  1 file changed, 6 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/xe/xe_vm_types.h b/drivers/gpu/drm/xe/xe_vm_types.h
> > index 2a8691a48c55..30beae541aca 100644
> > --- a/drivers/gpu/drm/xe/xe_vm_types.h
> > +++ b/drivers/gpu/drm/xe/xe_vm_types.h
> > @@ -51,11 +51,12 @@ struct xe_vma {
> >  		struct list_head destroy;
> >  	} combined_links;
> >  
> > -	/** @destroy_cb: callback to destroy VMA when unbind job is done */
> > -	struct dma_fence_cb destroy_cb;
> > -
> > -	/** @destroy_work: worker to destroy this BO */
> > -	struct work_struct destroy_work;
> > +	union {
> > +		/** @destroy_cb: callback to destroy VMA when unbind job is done */
> > +		struct dma_fence_cb destroy_cb;
> > +		/** @destroy_work: worker to destroy this BO */
> > +		struct work_struct destroy_work;
> > +	};
> >  
> >  	/** @userptr: user pointer state */
> >  	struct {
> > -- 
> > 2.34.1
> >