netdev - Re: [PATCH V2 net] net: mana: Fix error handling in mana_create

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Message-ID: <20240829084358.GA15997@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date: Thu, 29 Aug 2024 01:43:58 -0700
From: Souradeep Chakrabarti <schakrabarti@...ux.microsoft.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
	decui@...rosoft.com, davem@...emloft.net, edumazet@...gle.com,
	pabeni@...hat.com, longli@...rosoft.com, yury.norov@...il.com,
	leon@...nel.org, cai.huoqing@...ux.dev, ssengar@...ux.microsoft.com,
	vkuznets@...hat.com, tglx@...utronix.de,
	linux-hyperv@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
	schakrabarti@...rosoft.com
Subject: Re: [PATCH V2 net] net: mana: Fix error handling in
 mana_create_txq/rxq's NAPI cleanup

On Tue, Aug 27, 2024 at 01:26:37PM -0700, Jakub Kicinski wrote:
> On Fri, 23 Aug 2024 02:44:29 -0700 Souradeep Chakrabarti wrote:
> > @@ -2023,14 +2024,17 @@ static void mana_destroy_rxq(struct mana_port_context *apc,
> >  
> >  	napi = &rxq->rx_cq.napi;
> >  
> > -	if (validate_state)
> > -		napi_synchronize(napi);
> > +	if (napi->dev == apc->ndev) {
> >  
> > -	napi_disable(napi);
> > +		if (validate_state)
> > +			napi_synchronize(napi);
> >  
> > -	xdp_rxq_info_unreg(&rxq->xdp_rxq);
> > +		napi_disable(napi);
> >  
> > -	netif_napi_del(napi);
> > +		netif_napi_del(napi);
> > +	}
> > +
> > +	xdp_rxq_info_unreg(&rxq->xdp_rxq);
> 
> Please don't use internal core state as a crutch for your cleanup.
> 
> IDK what "validate_state" stands for, but it gives you all the info you
> need on Rx. On Rx NAPI registration happens as the last stage of rxq
> activation, once nothing can fail. And the "cleanup" path calls destroy
> with validate_state=false. The only other caller passes true.
> 
> So you can rewrite this as:
> 
> 	if (validate_state) { /* rename it maybe? */
> 		napi_disable(napi);
> 		...
> 	}
> 	xdp_rxq_info_unreg(&rxq->xdp_rxq);
> 
> You can take similar approach with Tx. Pass a bool which tells the
> destroy function whether NAPI has been registered.
Thanks Jakub for the suggestion. I have changed the implementation
in the V3. I have added a new txq and rxq structure attribute to check
that per queue napi is initialized.
The use of a local flag like validate_state will not be possible with
current design of txq destroy function, as it uses the hole vport
and loops for all the queues for that port.
-
Souradeep
> -- 
> pw-bot: cr