netdev - Re: [PATCH] net: page_pool: fix refcounting issues with fragmented allocation

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Date:   Thu, 26 Jan 2023 19:43:22 +0100
From:   Felix Fietkau <nbd@....name>
To:     Alexander H Duyck <alexander.duyck@...il.com>
Cc:     Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        netdev@...r.kernel.org, Jesper Dangaard Brouer <hawk@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        linux-kernel@...r.kernel.org, Yunsheng Lin <linyunsheng@...wei.com>
Subject: Re: [PATCH] net: page_pool: fix refcounting issues with fragmented
 allocation

On 26.01.23 19:38, Alexander H Duyck wrote:
> Okay, I think that tells me exactly what is going on. Can you give the
> change below a try and see if it solves the problem for you.
> 
> I think what is happening is that after you are reassigning the frags
> they are getting merged into GRO frames where the head may have
> pp_recycle set. As a result I think the pages are getting recycled when
> they should be just freed via put_page.
> 
> I'm suspecting this wasn't an issue up until now as I don't believe
> there are any that are running in a mixed mode where they have both
> pp_recycle and non-pp_recycle skbs coming from the same device.
> 
> diff --git a/net/core/gro.c b/net/core/gro.c
> index 506f83d715f8..4bac7ea6e025 100644
> --- a/net/core/gro.c
> +++ b/net/core/gro.c
> @@ -162,6 +162,15 @@ int skb_gro_receive(struct sk_buff *p, struct
> sk_buff *skb)
>   	struct sk_buff *lp;
>   	int segs;
>   
> +	/* Do not splice page pool based packets w/ non-page pool
> +	 * packets. This can result in reference count issues as page
> +	 * pool pages will not decrement the reference count and will
> +	 * instead be immediately returned to the pool or have frag
> +	 * count decremented.
> +	 */
> +	if (p->pp_recycle != skb->pp_recycle)
> +		return -ETOOMANYREFS;
> +
>   	/* pairs with WRITE_ONCE() in netif_set_gro_max_size() */
>   	gro_max_size = READ_ONCE(p->dev->gro_max_size);
>   
That works, thanks!

- Felix