Re: [PATCH v3 6/9] dma-buf/fence-array: Add fence deadline support

[Christian König]

Am 08.09.21 um 20:00 schrieb Daniel Vetter:
> On Fri, Sep 03, 2021 at 11:47:57AM -0700, Rob Clark wrote:
> > From: Rob Clark <robdclark@xxxxxxxxxxxx>
> >
> > Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
> > ---
> >   drivers/dma-buf/dma-fence-array.c | 11 +++++++++++
> >   1 file changed, 11 insertions(+)
> >
> > diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c
> > index d3fbd950be94..8d194b09ee3d 100644
> > --- a/drivers/dma-buf/dma-fence-array.c
> > +++ b/drivers/dma-buf/dma-fence-array.c
> > @@ -119,12 +119,23 @@ static void dma_fence_array_release(struct dma_fence *fence)
> >   	dma_fence_free(fence);
> >   }
> >   
> > +static void dma_fence_array_set_deadline(struct dma_fence *fence,
> > +					 ktime_t deadline)
> > +{
> > +	struct dma_fence_array *array = to_dma_fence_array(fence);
> > +	unsigned i;
> > +
> > +	for (i = 0; i < array->num_fences; ++i)
> > +		dma_fence_set_deadline(array->fences[i], deadline);
> Hm I wonder whether this can go wrong, and whether we need Christian's
> massive fence iterator that I've seen flying around. If you nest these
> things too much it could all go wrong I think. I looked at other users
> which inspect dma_fence_array and none of them have a risk for unbounded
> recursion.

That should work fine or at least doesn't add anything new which could 
go boom.

The dma_fence_array() can't contain other dma_fence_array or 
dma_fence_chain objects or it could end up in a recursion and corrupt 
the kernel stack.

That's a well known limitation for other code paths as well.

So Reviewed-by: Christian König <christian.koenig@xxxxxxx> for this one.

Regards,
Christian.

> Maybe check with Christian.
> -Daniel
>
>
> > +}
> > +
> >   const struct dma_fence_ops dma_fence_array_ops = {
> >   	.get_driver_name = dma_fence_array_get_driver_name,
> >   	.get_timeline_name = dma_fence_array_get_timeline_name,
> >   	.enable_signaling = dma_fence_array_enable_signaling,
> >   	.signaled = dma_fence_array_signaled,
> >   	.release = dma_fence_array_release,
> > +	.set_deadline = dma_fence_array_set_deadline,
> >   };
> >   EXPORT_SYMBOL(dma_fence_array_ops);
> >   
> > --
> > 2.31.1