linux-kernel - Re: [PATCH net v2] tcp: reset tp->sacked

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Date:   Thu, 27 Oct 2022 19:04:29 +0800
From:   "luwei (O)" <luwei32@...wei.com>
To:     <edumazet@...gle.com>, <davem@...emloft.net>,
        <yoshfuji@...ux-ipv6.org>, <dsahern@...nel.org>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <xemul@...allels.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <ovzxemul@...il.com>, <ptikhomirov@...tuozzo.com>,
        <den@...tuozzo.com>
Subject: Re: [PATCH net v2] tcp: reset tp->sacked_out when sack is enabled

please ignore this patch， I forgot to change the title

在 2022/10/27 7:49 PM, Lu Wei 写道:
> If setsockopt with option name of TCP_REPAIR_OPTIONS and opt_code
> of TCPOPT_SACK_PERM is called to enable sack after data is sent
> and before data is acked, it will trigger a warning in function
> tcp_verify_left_out() as follows:
>
> ============================================
> WARNING: CPU: 8 PID: 0 at net/ipv4/tcp_input.c:2132
> tcp_timeout_mark_lost+0x154/0x160
> tcp_enter_loss+0x2b/0x290
> tcp_retransmit_timer+0x50b/0x640
> tcp_write_timer_handler+0x1c8/0x340
> tcp_write_timer+0xe5/0x140
> call_timer_fn+0x3a/0x1b0
> __run_timers.part.0+0x1bf/0x2d0
> run_timer_softirq+0x43/0xb0
> __do_softirq+0xfd/0x373
> __irq_exit_rcu+0xf6/0x140
>
> This warning occurs in several steps:
> Step1. If sack is not enabled, when server receives dup-ack,
>         it calls tcp_add_reno_sack() to increase tp->sacked_out.
>
> Step2. Setsockopt() is called to enable sack
>
> Step3. The retransmit timer expires, it calls tcp_timeout_mark_lost()
>         to increase tp->lost_out but not clear tp->sacked_out because
>         sack is enabled and tcp_is_reno() is false.
>
> So tp->left_out is increased repeatly in Step1 and Step3 and it is
> greater than tp->packets_out and trigger the warning. In function
> tcp_timeout_mark_lost(), tp->sacked_out will be cleared if Step2 not
> happen and the warning will not be triggered. As suggested by Denis
> and Eric, TCP_REPAIR_OPTIONS should be prohibited if data was already
> sent.
>
> socket-tcp tests in CRIU has been tested as follows:
> $ sudo ./test/zdtm.py run -t zdtm/static/socket-tcp*  --keep-going \
>         --ignore-taint
>
> socket-tcp* represent all socket-tcp tests in test/zdtm/static/.
>
> Fixes: b139ba4e90dc ("tcp: Repair connection-time negotiated parameters")
> Signed-off-by: Lu Wei <luwei32@...wei.com>
> ---
>   net/ipv4/tcp.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index ef14efa1fb70..ef876e70f7fe 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -3647,7 +3647,7 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
>   	case TCP_REPAIR_OPTIONS:
>   		if (!tp->repair)
>   			err = -EINVAL;
> -		else if (sk->sk_state == TCP_ESTABLISHED)
> +		else if (sk->sk_state == TCP_ESTABLISHED && !tp->packets_out)
>   			err = tcp_repair_options_est(sk, optval, optlen);
>   		else
>   			err = -EPERM;

-- 
Best Regards,
Lu Wei