netdev - Re: [net PATCH] skb: Do mix page pool and page referenced frags in GRO

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Date:   Mon, 30 Jan 2023 17:49:27 +0100
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        Alexander Duyck <alexander.duyck@...il.com>
Cc:     brouer@...hat.com, nbd@....name, davem@...emloft.net,
        edumazet@...gle.com, hawk@...nel.org, ilias.apalodimas@...aro.org,
        linux-kernel@...r.kernel.org, linyunsheng@...wei.com,
        lorenzo@...nel.org, netdev@...r.kernel.org, pabeni@...hat.com
Subject: Re: [net PATCH] skb: Do mix page pool and page referenced frags in
 GRO



On 27/01/2023 00.13, Jakub Kicinski wrote:
> On Thu, 26 Jan 2023 11:06:59 -0800 Alexander Duyck wrote:
>> From: Alexander Duyck<alexanderduyck@...com>
>>
>> GSO should not merge page pool recycled frames with standard reference
>> counted frames. Traditionally this didn't occur, at least not often.
>> However as we start looking at adding support for wireless adapters there
>> becomes the potential to mix the two due to A-MSDU repartitioning frames in
>> the receive path. There are possibly other places where this may have
>> occurred however I suspect they must be few and far between as we have not
>> seen this issue until now.
>>
>> Fixes: 53e0961da1c7 ("page_pool: add frag page recycling support in page pool")
>> Reported-by: Felix Fietkau<nbd@....name>
>> Signed-off-by: Alexander Duyck<alexanderduyck@...com>
> Exciting investigation!
> Felix, out of curiosity - the impact of loosing GRO on performance is
> not significant enough to care?  We could possibly try to switch to
> using the frag list if we can't merge into frags safely.

Using the frag list sounds scary, because we recently learned that
kfree_skb_list requires all SKBs on the list to have same refcnt (else
the walking of the list can lead to other bugs).

--Jesper