netdev - Re: [PATCH] net: drop skbs in napi->rx_list when removing the napi context.

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Date:   Fri, 13 Aug 2021 03:17:18 +0800
From:   Phi Nguyen <phind.uet@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        kpsingh@...nel.org, Antoine Tenart <atenart@...nel.org>,
        Alexander Lobakin <alobakin@...me>,
        Wei Wang <weiwan@...gle.com>, Taehee Yoo <ap420073@...il.com>,
        Björn Töpel <bjorn@...nel.org>,
        memxor@...il.com, netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        syzbot+989efe781c74de1ddb54@...kaller.appspotmail.com
Subject: Re: [PATCH] net: drop skbs in napi->rx_list when removing the napi
 context.

On 8/12/2021 3:07 PM, Eric Dumazet wrote:
> Also I object to this fix.
> 
> If packets have been stored temporarily in GRO, they should be
> released at some point,
> normally at the end of a napi poll.
> 
> By released, I mean that these packets should reach the upper stack,
> instead of being dropped without
> any notification.
> 
> It seems a call to gro_normal_list() is missing somewhere.
> 
> Can you find where ?
> 
> Thanks !
> H Eric,

I think the location that should have a call to gro_normal_list() is 
__netif_napi_del(). Let say, if the driver call a function that lead to 
gro_normal_one(), and add a skb to the rx_list while the napi poll is 
not scheduled, and the driver remove the napi context before a napi poll 
could be triggered, then the added skb will be lost.

Actually, this was the first solution that I tried with syzbot (It 
passed the test too).
Best regards,
Phi