linux-kernel - Re: [PATCH] tcp: another fix of uncloning packets before mangling them

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Date:   Tue, 28 Aug 2018 00:36:37 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     wen.yang99@....com.cn
Cc:     David Miller <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, jiang.biao2@....com.cn,
        zhong.weidong@....com.cn, liu.bo9@....com.cn
Subject: Re: [PATCH] tcp: another fix of uncloning packets before mangling them

On Tue, Aug 28, 2018 at 12:32 AM Wen Yang <wen.yang99@....com.cn> wrote:
>
> The following warning was caught：
>
> [937151.638394] Call Trace:
> [937151.638401]  [<ffffffff8163f2f6>] dump_stack+0x19/0x1b
> [937151.638405]  [<ffffffff8107dd70>] warn_slowpath_common+0x70/0xb0
> [937151.638407]  [<ffffffff8107deba>] warn_slowpath_null+0x1a/0x20
> [937151.638410]  [<ffffffff8158bb7b>] tcp_set_skb_tso_segs+0xeb/0x100
> [937151.638412]  [<ffffffff8158bbc7>] tcp_init_tso_segs+0x37/0x50
> [937151.638414]  [<ffffffff8158d7b9>] tcp_write_xmit+0x1d9/0xce0
> [937151.638417]  [<ffffffff8158e53e>] __tcp_push_pending_frames+0x2e/0xc0
> [937151.638419]  [<ffffffff8157cf3c>] tcp_push+0xec/0x120
> [937151.638421]  [<ffffffff81580728>] tcp_sendmsg+0xc8/0xc20
> [937151.638424]  [<ffffffff815aae24>] inet_sendmsg+0x64/0xb0
> [937151.638428]  [<ffffffff810b9565>] ? check_preempt_curr+0x75/0xa0
> [937151.638434]  [<ffffffff81519917>] sock_aio_write+0x157/0x180
> [937151.638437]  [<ffffffff811e267d>] do_sync_write+0x8d/0xd0
> [937151.638440]  [<ffffffff811e2f95>] vfs_write+0x1b5/0x1e0
> [937151.638442]  [<ffffffff811e393f>] SyS_write+0x7f/0xe0
> [937151.638445]  [<ffffffff816513fd>] system_call_fastpath+0x16/0x1b
>
> According commit c52e2421f736 ("tcp: must unclone packets before
> mangling them"), TCP stack should make sure it owns skbs before
> mangling them.
> And there is another place where skb_unclone() is needed. This patch
> fix that.
>
> Signed-off-by: Wen Yang <wen.yang99@....com.cn>
> Tested-by: Liu Bo <liu.bo9@....com.cn>
> Reviewed-by: Jiang Biao <jiang.biao2@....com.cn>
> ---
>  net/ipv4/tcp_output.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 597dbd7..fbe8140 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -1793,6 +1793,9 @@ static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
>         int tso_segs = tcp_skb_pcount(skb);
>

Certainly not needed.

TCP stack owns its packets, as long they were never sent (not yet in
retransmit queue)

You probably are using an old kernel, missing some backport...