netdev - Re: [PATCH v2 net-next] net: add per-cpu storage and net->core

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Message-ID: <813acfa36558d355e6b56b17bd6bce1c67f77296.camel@redhat.com>
Date:   Thu, 10 Mar 2022 10:26:09 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        jeffreyji <jeffreyji@...gle.com>,
        Brian Vazquez <brianvv@...gle.com>
Subject: Re: [PATCH v2 net-next] net: add per-cpu storage and net->core_stats

Hello,

On Wed, 2022-03-09 at 16:46 -0800, Eric Dumazet wrote:
> @@ -10282,6 +10282,24 @@ void netdev_stats_to_stats64(struct rtnl_link_stats64 *stats64,
>  }
>  EXPORT_SYMBOL(netdev_stats_to_stats64);
>  
> +struct net_device_core_stats *netdev_core_stats_alloc(struct net_device *dev)
> +{
> +	struct net_device_core_stats __percpu *p;
> +
> +	p = alloc_percpu_gfp(struct net_device_core_stats,
> +			     GFP_ATOMIC | __GFP_NOWARN);
> +
> +	if (p && cmpxchg(&dev->core_stats, NULL, p))
> +		free_percpu(p);
> +
> +	p = dev->core_stats;

Don't we need a READ_ONCE() here? if the allocation fails (!p) there is
no memory barrier.

Thanks!

Paolo