linux-kernel - Re: Problem in pfmemalloc skb handling in net/core/dev.c

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Date:   Mon, 12 Apr 2021 13:40:54 -0700
From:   Xie He <xie.he.0141@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Mel Gorman <mgorman@...e.de>, jslaby@...e.cz,
        Neil Brown <neilb@...e.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Mike Christie <michaelc@...wisc.edu>,
        Eric B Munson <emunson@...bm.net>,
        Sebastian Andrzej Siewior <sebastian@...akpoint.cc>,
        Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Problem in pfmemalloc skb handling in net/core/dev.c

On Fri, Apr 9, 2021 at 12:12 PM Xie He <xie.he.0141@...il.com> wrote:
>
> This is exactly what I'm talking about. "skb_pfmemalloc_protocol"
> cannot guarantee pfmemalloc skbs are not delivered to unrelated
> protocols, because "__netif_receive_skb" will sometimes treat
> pfmemalloc skbs as normal skbs.

> I'm not sure if you understand what I'm saying. Please look at the
> code of "__netif_receive_skb" and see what will happen when
> "sk_memalloc_socks()" is false and "skb_pfmemalloc(skb)" is true.

Do you see the problem now? Just think what happens when
"skb_pfmemalloc(skb)" is true and "sk_memalloc_socks()" has just
changed to "false", and whether in this case "skb_pfmemalloc_protocol"
still takes any effect.