netdev - Re: [PATCH v6 08/15] net: add helper executing custom callback from napi

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Message-ID: <cd9c2290-f874-49e6-bc99-5336a096cffb@redhat.com>
Date: Mon, 21 Oct 2024 16:25:25 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: David Wei <dw@...idwei.uk>, io-uring@...r.kernel.org,
 netdev@...r.kernel.org
Cc: Jens Axboe <axboe@...nel.dk>, Pavel Begunkov <asml.silence@...il.com>,
 Jakub Kicinski <kuba@...nel.org>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jesper Dangaard Brouer
 <hawk@...nel.org>, David Ahern <dsahern@...nel.org>,
 Mina Almasry <almasrymina@...gle.com>,
 Stanislav Fomichev <stfomichev@...il.com>, Joe Damato <jdamato@...tly.com>,
 Pedro Tammela <pctammela@...atatu.com>
Subject: Re: [PATCH v6 08/15] net: add helper executing custom callback from
 napi

Hi,

On 10/16/24 20:52, David Wei wrote:
> @@ -6503,6 +6511,41 @@ void napi_busy_loop(unsigned int napi_id,
>  }
>  EXPORT_SYMBOL(napi_busy_loop);
>  
> +void napi_execute(unsigned napi_id,
> +		  void (*cb)(void *), void *cb_arg)
> +{
> +	struct napi_struct *napi;
> +	void *have_poll_lock = NULL;

Minor nit: please respect the reverse x-mas tree order.

> +
> +	guard(rcu)();

Since this will land into net core code, please use the explicit RCU
read lock/unlock:

https://elixir.bootlin.com/linux/v6.12-rc3/source/Documentation/process/maintainer-netdev.rst#L387

> +	napi = napi_by_id(napi_id);
> +	if (!napi)
> +		return;
> +
> +	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
> +		preempt_disable();
> +
> +	for (;;) {
> +		local_bh_disable();
> +
> +		if (napi_state_start_busy_polling(napi, 0)) {
> +			have_poll_lock = netpoll_poll_lock(napi);
> +			cb(cb_arg);
> +			local_bh_enable();
> +			busy_poll_stop(napi, have_poll_lock, 0, 1);
> +			break;
> +		}
> +
> +		local_bh_enable();
> +		if (unlikely(need_resched()))
> +			break;
> +		cpu_relax();

Don't you need a 'loop_end' condition here?

Side notes not specifically related to this patch: I likely got lost in
previous revision, but it's unclear to me which is the merge plan here,
could you please (re-)word it?

Thanks!

Paolo