Re: [PATCH 03/23] dma-buf: add dma_resv_get_singleton v2

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Apr 01, 2022 at 10:21:22AM +0200, Christian König wrote:
> Daniel any more comments on this one here?
> 
> It's the prerequisite to a bunch of other patches and I would like to get it
> out of my feet.

Apologies for the miss, I thought I've r-b stamped this one already.

> 
> Thanks,
> Christian.
> 
> Am 21.03.22 um 14:58 schrieb Christian König:
> > Add a function to simplify getting a single fence for all the fences in
> > the dma_resv object.
> > 
> > v2: fix ref leak in error handling
> > 
> > Signed-off-by: Christian König <christian.koenig@amd.com>
> > ---
> >   drivers/dma-buf/dma-resv.c | 52 ++++++++++++++++++++++++++++++++++++++
> >   include/linux/dma-resv.h   |  2 ++
> >   2 files changed, 54 insertions(+)
> > 
> > diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
> > index 5001e9b4420a..c09fd8da0c85 100644
> > --- a/drivers/dma-buf/dma-resv.c
> > +++ b/drivers/dma-buf/dma-resv.c
> > @@ -34,6 +34,7 @@
> >    */
> >   #include <linux/dma-resv.h>
> > +#include <linux/dma-fence-array.h>
> >   #include <linux/export.h>
> >   #include <linux/mm.h>
> >   #include <linux/sched/mm.h>
> > @@ -650,6 +651,57 @@ int dma_resv_get_fences(struct dma_resv *obj, bool write,
> >   }
> >   EXPORT_SYMBOL_GPL(dma_resv_get_fences);
> > +/**
> > + * dma_resv_get_singleton - Get a single fence for all the fences
> > + * @obj: the reservation object
> > + * @write: true if we should return all fences
> > + * @fence: the resulting fence
> > + *
> > + * Get a single fence representing all the fences inside the resv object.
> > + * Returns either 0 for success or -ENOMEM.
> > + *
> > + * Warning: This can't be used like this when adding the fence back to the resv
> > + * object since that can lead to stack corruption when finalizing the
> > + * dma_fence_array.

Please add the standard boilerplate here:

Returns 0 on success and negative error values on failure.

> > + */
> > +int dma_resv_get_singleton(struct dma_resv *obj, bool write,
> > +			   struct dma_fence **fence)
> > +{
> > +	struct dma_fence_array *array;
> > +	struct dma_fence **fences;
> > +	unsigned count;
> > +	int r;
> > +
> > +	r = dma_resv_get_fences(obj, write, &count, &fences);

Deep down in here we already have the dma_resv_assert_held, so I'm happy.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> > +        if (r)
> > +		return r;
> > +
> > +	if (count == 0) {
> > +		*fence = NULL;
> > +		return 0;
> > +	}
> > +
> > +	if (count == 1) {
> > +		*fence = fences[0];
> > +		kfree(fences);
> > +		return 0;
> > +	}
> > +
> > +	array = dma_fence_array_create(count, fences,
> > +				       dma_fence_context_alloc(1),
> > +				       1, false);
> > +	if (!array) {
> > +		while (count--)
> > +			dma_fence_put(fences[count]);
> > +		kfree(fences);
> > +		return -ENOMEM;
> > +	}
> > +
> > +	*fence = &array->base;
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(dma_resv_get_singleton);
> > +
> >   /**
> >    * dma_resv_wait_timeout - Wait on reservation's objects
> >    * shared and/or exclusive fences.
> > diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
> > index 202cc65d0621..08512c1e215d 100644
> > --- a/include/linux/dma-resv.h
> > +++ b/include/linux/dma-resv.h
> > @@ -449,6 +449,8 @@ void dma_resv_replace_fences(struct dma_resv *obj, uint64_t context,
> >   void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence);
> >   int dma_resv_get_fences(struct dma_resv *obj, bool write,
> >   			unsigned int *num_fences, struct dma_fence ***fences);
> > +int dma_resv_get_singleton(struct dma_resv *obj, bool write,
> > +			   struct dma_fence **fence);
> >   int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src);
> >   long dma_resv_wait_timeout(struct dma_resv *obj, bool wait_all, bool intr,
> >   			   unsigned long timeout);
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch