Re: [PATCH 06/26] dma-buf: use new iterator in dma_resv_test_signaled

From: Daniel Vetter <daniel@ffwll.ch>
To: "Christian König" <ckoenig.leichtzumerken@gmail.com>
Cc: linaro-mm-sig@lists.linaro.org, dri-devel@lists.freedesktop.org,
	linux-media@vger.kernel.org, intel-gfx@lists.freedesktop.org,
	daniel@ffwll.ch
Subject: Re: [PATCH 06/26] dma-buf: use new iterator in dma_resv_test_signaled
Date: Fri, 17 Sep 2021 16:45:28 +0200	[thread overview]
Message-ID: <YUSqCIxUbkk0qCO9@phenom.ffwll.local> (raw)
In-Reply-To: <20210917123513.1106-7-christian.koenig@amd.com>

On Fri, Sep 17, 2021 at 02:34:53PM +0200, Christian König wrote:
> This makes the function much simpler since the complex
> retry logic is now handled elsewhere.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
>  drivers/dma-buf/dma-resv.c | 56 ++++++--------------------------------
>  1 file changed, 9 insertions(+), 47 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
> index c7db553ab115..d8f428ddaedd 100644
> --- a/drivers/dma-buf/dma-resv.c
> +++ b/drivers/dma-buf/dma-resv.c
> @@ -593,22 +593,6 @@ long dma_resv_wait_timeout(struct dma_resv *obj, bool wait_all, bool intr,
>  EXPORT_SYMBOL_GPL(dma_resv_wait_timeout);
>  
>  
> -static inline int dma_resv_test_signaled_single(struct dma_fence *passed_fence)
> -{
> -	struct dma_fence *fence, *lfence = passed_fence;
> -	int ret = 1;
> -
> -	if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &lfence->flags)) {
> -		fence = dma_fence_get_rcu(lfence);
> -		if (!fence)
> -			return -1;
> -
> -		ret = !!dma_fence_is_signaled(fence);
> -		dma_fence_put(fence);
> -	}
> -	return ret;
> -}
> -
>  /**
>   * dma_resv_test_signaled - Test if a reservation object's fences have been
>   * signaled.
> @@ -625,43 +609,21 @@ static inline int dma_resv_test_signaled_single(struct dma_fence *passed_fence)
>   */
>  bool dma_resv_test_signaled(struct dma_resv *obj, bool test_all)
>  {
> +	struct dma_resv_iter cursor;
>  	struct dma_fence *fence;
> -	unsigned int seq;
> -	int ret;
>  
>  	rcu_read_lock();
> -retry:
> -	ret = true;
> -	seq = read_seqcount_begin(&obj->seq);
> -
> -	if (test_all) {
> -		struct dma_resv_list *fobj = dma_resv_shared_list(obj);
> -		unsigned int i, shared_count;
> -
> -		shared_count = fobj ? fobj->shared_count : 0;
> -		for (i = 0; i < shared_count; ++i) {
> -			fence = rcu_dereference(fobj->shared[i]);
> -			ret = dma_resv_test_signaled_single(fence);
> -			if (ret < 0)
> -				goto retry;
> -			else if (!ret)
> -				break;
> +	dma_resv_iter_begin(&cursor, obj, test_all);
> +	dma_resv_for_each_fence_unlocked(&cursor, fence) {
> +		if (!dma_fence_is_signaled(fence)) {

Should we be extremely clever and document that the iterator already
filters out unsignalled fences? We could rely on that here :-) Otoh we
don't want to make the full is_signalled check in that iterator, so this
makes sense.

Again rcu_read_lock into the iterators pls. With that:

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

> +			dma_resv_iter_end(&cursor);
> +			rcu_read_unlock();
> +			return false;
>  		}
>  	}
> -
> -	fence = dma_resv_excl_fence(obj);
> -	if (ret && fence) {
> -		ret = dma_resv_test_signaled_single(fence);
> -		if (ret < 0)
> -			goto retry;
> -
> -	}
> -
> -	if (read_seqcount_retry(&obj->seq, seq))
> -		goto retry;
> -
> +	dma_resv_iter_end(&cursor);
>  	rcu_read_unlock();
> -	return ret;
> +	return true;
>  }
>  EXPORT_SYMBOL_GPL(dma_resv_test_signaled);
>  
> -- 
> 2.25.1
> 

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