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From: Eric Dumazet <edumazet@google.com>
Date: Tue, 14 Mar 2017 08:09:40 -0700
Message-ID: <CANn89iLB8UvDCQVoWZHeDKXX6te0x7C9NGsoJ_X9+8cF+mm0cg@mail.gmail.com>
Subject: Re: net: deadlock between ip_expire/sch_direct_xmit
To: Paolo Abeni <pabeni@redhat.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>, David Miller <davem@davemloft.net>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        James Morris <jmorris@namei.org>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Patrick McHardy <kaber@trash.net>, netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Jamal Hadi Salim <jhs@mojatatu.com>,
        syzkaller <syzkaller@googlegroups.com>
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On Tue, Mar 14, 2017 at 8:03 AM, Paolo Abeni <pabeni@redhat.com> wrote:

> I'm wondering if we really need to keep the fragment queue lock held
> while sending the icmp packet ? we hold a reference to the struct, so
> it can't be deleted, and AFAICS after ipq_kill() nobody else could
> access/modify that queue.
>
> That lock is there pretty much forever, but perhaps is only a leftover
> and we can release it just after ipq_kill() ?

Maybe, but for peace of mind I would make sure this code path owns the
skb (head) before releasing the lock.

Seems something to try for net-next ?