Re: [PATCH 02/26] dma-buf: add dma_resv_for_each_fence

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Sep 17, 2021 at 02:34:49PM +0200, Christian König wrote:
> A simpler version of the iterator to be used when the dma_resv object is
> locked.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
>  drivers/dma-buf/dma-resv.c | 33 +++++++++++++++++++++++++++++++++
>  include/linux/dma-resv.h   | 17 +++++++++++++++++
>  2 files changed, 50 insertions(+)
> 
> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
> index 3e77cad2c9d4..a3c79a99fb44 100644
> --- a/drivers/dma-buf/dma-resv.c
> +++ b/drivers/dma-buf/dma-resv.c
> @@ -384,6 +384,39 @@ struct dma_fence *dma_resv_iter_walk_unlocked(struct dma_resv_iter *cursor,
>  }
>  EXPORT_SYMBOL_GPL(dma_resv_iter_walk_unlocked);
>  
> +/**
> + * dma_resv_iter_walk - walk over fences in a dma_resv obj
> + * @cursor: cursor to record the current position
> + * @first: if we should start over
> + *
> + * Return all the fences in the dma_resv object while holding the
> + * dma_resv::lock.
> + */
> +struct dma_fence *dma_resv_iter_walk(struct dma_resv_iter *cursor, bool first)
> +{
> +	dma_resv_assert_held(cursor->obj);
> +
> +	cursor->is_first = first;
> +	if (first) {
> +		struct dma_fence *fence;
> +
> +		cursor->index = -1;
> +		cursor->fences = dma_resv_shared_list(cursor->obj);
> +
> +		fence = dma_resv_excl_fence(cursor->obj);
> +		if (fence)
> +			return fence;
> +	}

I think you can still use the shared iter_begin/end functions even with my
suggestions for patch 1, but would mean changes here too.

> +
> +	if (!cursor->all_fences || !cursor->fences ||
> +	    ++cursor->index >= cursor->fences->shared_count)
> +		return NULL;
> +
> +	return rcu_dereference_protected(cursor->fences->shared[cursor->index],
> +					 dma_resv_held(cursor->obj));
> +}
> +EXPORT_SYMBOL_GPL(dma_resv_iter_walk);
> +
>  /**
>   * dma_resv_copy_fences - Copy all fences from src to dst.
>   * @dst: the destination reservation object
> diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
> index 693d16117153..8c968f8c9d33 100644
> --- a/include/linux/dma-resv.h
> +++ b/include/linux/dma-resv.h
> @@ -179,6 +179,7 @@ struct dma_resv_iter {
>  
>  struct dma_fence *dma_resv_iter_walk_unlocked(struct dma_resv_iter *cursor,
>  					      bool first);
> +struct dma_fence *dma_resv_iter_walk(struct dma_resv_iter *cursor, bool first);
>  
>  /**
>   * dma_resv_iter_begin - initialize a dma_resv_iter object
> @@ -233,6 +234,22 @@ static inline bool dma_resv_iter_is_exclusive(struct dma_resv_iter *cursor)
>  	for (fence = dma_resv_iter_walk_unlocked(cursor, true);		\
>  	     fence; fence = dma_resv_iter_walk_unlocked(cursor, false))
>  
> +/**
> + * dma_resv_for_each_fence - fence iterator
> + * @cursor: a struct dma_resv_iter pointer
> + * @obj: a dma_resv object pointer
> + * @all_fences: true if all fences should be returned
> + * @fence: the current fence
> + *
> + * Iterate over the fences in a struct dma_resv object while holding the
> + * dma_resv::lock. @all_fences controls if the shared fences are returned as

&dma_resv.lock is how you reference struct members in kerneldoc. I think
you had this also in patch 1.

> + * well. The cursor initialisation is part of the iterator.

Please also link to the iter_begin/end functions here.

Aside from doc nits and obviously changes due to changes in patch 1 (if we
do them), this looks good.
-Daniel

> + */
> +#define dma_resv_for_each_fence(cursor, obj, all_fences, fence)	\
> +	for (dma_resv_iter_begin(cursor, obj, all_fences),	\
> +	     fence = dma_resv_iter_walk(cursor, true); fence;	\
> +	     fence = dma_resv_iter_walk(cursor, false))
> +
>  #define dma_resv_held(obj) lockdep_is_held(&(obj)->lock.base)
>  #define dma_resv_assert_held(obj) lockdep_assert_held(&(obj)->lock.base)
>  
> -- 
> 2.25.1
> 

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