netdev - Re: [PATCH v4 7/8] io_uring/zcrx: add refcount to ifq and remove ifq->ctx

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Message-ID: <b0890420-6897-4ef9-a15a-8b9721ce85d0@gmail.com>
Date: Thu, 30 Oct 2025 15:24:33 +0000
From: Pavel Begunkov <asml.silence@...il.com>
To: David Wei <dw@...idwei.uk>, io-uring@...r.kernel.org,
 netdev@...r.kernel.org
Cc: Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v4 7/8] io_uring/zcrx: add refcount to ifq and remove
 ifq->ctx

On 10/29/25 16:16, Pavel Begunkov wrote:
> On 10/29/25 15:22, Pavel Begunkov wrote:
>> On 10/28/25 17:46, David Wei wrote:
...>>>   void io_unregister_zcrx_ifqs(struct io_ring_ctx *ctx)
>>>   {
>>>       struct io_zcrx_ifq *ifq;
>>> @@ -743,7 +730,10 @@ void io_unregister_zcrx_ifqs(struct io_ring_ctx *ctx)
>>>           }
>>>           if (!ifq)
>>>               break;
>>> -        io_zcrx_ifq_free(ifq);
>>> +        if (refcount_dec_and_test(&ifq->refs)) {
>>> +            io_zcrx_scrub(ifq);
>>> +            io_zcrx_ifq_free(ifq);
>>> +        }
>>>       }
>>>       xa_destroy(&ctx->zcrx_ctxs);
>>> @@ -894,15 +884,11 @@ static int io_pp_zc_init(struct page_pool *pp)
>>>       if (ret)
>>>           return ret;
>>> -    percpu_ref_get(&ifq->ctx->refs);
>>>       return 0;
>>
>> refcount_inc();
> 
> Which would add another ref cycle problem, the same that IIRC
> was solved with two step shutdown + release. I'll take a closer
> look.

The simplest solution is to keep the two 2 level release and
split refcounting for sharing. It's still better as now
shutdown can be folded into the io_uring ifq unregstration
helper.

https://github.com/isilence/linux.git zcrx/zcrx-sharing
https://github.com/isilence/liburing.git zcrx/zcrx-sharing

I fixed up synchronisation and drafted the export/import via
a file part, take a look.

-- 
Pavel Begunkov