Re: [PATCH 1/5] io_uring/zcrx: notify user when out of buffers

On 4/22/26 12:25, Clément Léger wrote:
> From: Pavel Begunkov <[email protected]>
...>   static inline struct page *io_zcrx_iov_page(const struct net_iov *niov)
>   {
>   	struct io_zcrx_area *area = io_zcrx_iov_to_area(niov);
> @@ -531,6 +541,7 @@ static struct io_zcrx_ifq *io_zcrx_ifq_alloc(struct io_ring_ctx *ctx)
>   
>   	ifq->if_rxq = -1;
>   	spin_lock_init(&ifq->rq.lock);
> +	spin_lock_init(&ifq->ctx_lock);
>   	mutex_init(&ifq->pp_lock);
>   	refcount_set(&ifq->refs, 1);
>   	refcount_set(&ifq->user_refs, 1);
> @@ -585,6 +596,11 @@ static void io_zcrx_ifq_free(struct io_zcrx_ifq *ifq)
>   	if (ifq->dev)
>   		put_device(ifq->dev);
>   
> +	scoped_guard(spinlock_bh, &ifq->ctx_lock) {
> +		if (ifq->master_ctx)
> +			percpu_ref_put(&ifq->master_ctx->refs);
> +	}
> +

Something very odd happened here. It's not my patch but rather an edited
squash of two other patches. This particular hunk creates a circular
dependency, i.e. io_uring waits for this reference to be put down before
destroying the zcrx instance that triggers io_zcrx_ifq_free.

-- 
Pavel Begunkov