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Date: Tue, 2 Mar 2010 16:16:59 +0300
From: sbs <gexlie@...il.com>
To: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Cc: Netdev <netdev@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: Panic at tcp_xmit_retransmit_queue
thank you very much, have stable running server for a week and it
seems that it works like a charm now, i havent detected any panics
since i apply the patch. although seems that the problem stops
ocurring cause i dont see any debug information through netconsole
On Mon, Feb 15, 2010 at 4:21 PM, Ilpo Järvinen
<ilpo.jarvinen@...sinki.fi> wrote:
> On Wed, 3 Feb 2010, Ilpo Järvinen wrote:
>
>> On Mon, 1 Feb 2010, sbs wrote:
>>
>> > actually removing netconsole from kernel didnt help.
>> > i found many guys with the same problem but with different hardware
>> > configurations here:
>> >
>> > freez in TCP stack :
>> > http://bugzilla.kernel.org/show_bug.cgi?id=14470
>> >
>> > is there someone who can investigate it?
>> >
>> >
>> > On Tue, Jan 19, 2010 at 7:13 PM, sbs <gexlie@...il.com> wrote:
>> > > We are hiting kernel panics on servers with nVidia MCP55 NICs once a day;
>> > > it appears usualy under a high network trafic ( around 10000Mbit/s) but
>> > > it is not a rule, it has happened even on low trafic.
>> > >
>> > > Servers are used as nginx+static content
>> > > On 2 equal servers this panic happens aprox 2 times a day depending on
>> > > network load. Machine completly freezes till the netconsole reboots.
>> > >
>> > > Kernel: 2.6.32.3
>> > >
>> > > what can it be? whats wrong with tcp_xmit_retransmit_queue() function ?
>> > > can anyone explain or fix?
>>
>> You might want to try with to debug patch below. It might even make the
>> box to survive the event (if I got it coded right).
>
> Here should be a better version of the debug patch, hopefully the infinite
> looping is now gone.
>
> --
> i.
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 383ce23..4672a30 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -2186,6 +2186,42 @@ static int tcp_can_forward_retransmit(struct sock *sk)
> return 1;
> }
>
> +static void print_queue(struct sock *sk, struct sk_buff *old, struct sk_buff *hole)
> +{
> + struct tcp_sock *tp = tcp_sk(sk);
> + struct sk_buff *skb, *prev;
> +
> + skb = tcp_write_queue_head(sk);
> + prev = (struct sk_buff *)(&sk->sk_write_queue);
> +
> + if (skb == NULL) {
> + printk("NULL head, pkts %u\n", tp->packets_out);
> + return;
> + }
> + printk("head %p tail %p sendhead %p oldhint %p now %p hole %p high %u\n",
> + tcp_write_queue_head(sk), tcp_write_queue_tail(sk),
> + tcp_send_head(sk), old, tp->retransmit_skb_hint, hole,
> + tp->retransmit_high);
> +
> + while (skb) {
> + printk("skb %p (%u-%u) next %p prev %p sacked %u\n",
> + skb, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
> + skb->next, skb->prev, TCP_SKB_CB(skb)->sacked);
> + if (prev != skb->prev)
> + printk("Inconsistent prev\n");
> +
> + if (skb == tcp_write_queue_tail(sk)) {
> + if (skb->next != (struct sk_buff *)(&sk->sk_write_queue))
> + printk("Improper next at tail\n");
> + return;
> + }
> +
> + prev = skb;
> + skb = skb->next;
> + }
> + printk("Encountered unexpected NULL\n");
> +}
> +
> /* This gets called after a retransmit timeout, and the initially
> * retransmitted data is acknowledged. It tries to continue
> * resending the rest of the retransmit queue, until either
> @@ -2194,12 +2230,15 @@ static int tcp_can_forward_retransmit(struct sock *sk)
> * based retransmit packet might feed us FACK information again.
> * If so, we use it to avoid unnecessarily retransmissions.
> */
> +static int caught_it = 0;
> +
> void tcp_xmit_retransmit_queue(struct sock *sk)
> {
> const struct inet_connection_sock *icsk = inet_csk(sk);
> struct tcp_sock *tp = tcp_sk(sk);
> struct sk_buff *skb;
> struct sk_buff *hole = NULL;
> + struct sk_buff *old = tp->retransmit_skb_hint;
> u32 last_lost;
> int mib_idx;
> int fwd_rexmitting = 0;
> @@ -2217,6 +2256,16 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
> last_lost = tp->snd_una;
> }
>
> +checknull:
> + if (skb == NULL) {
> + if (!caught_it)
> + print_queue(sk, old, hole);
> + caught_it++;
> + if (net_ratelimit())
> + printk("Errors caught so far %u\n", caught_it);
> + return;
> + }
> +
> tcp_for_write_queue_from(skb, sk) {
> __u8 sacked = TCP_SKB_CB(skb)->sacked;
>
> @@ -2257,7 +2306,7 @@ begin_fwd:
> } else if (!(sacked & TCPCB_LOST)) {
> if (hole == NULL && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
> hole = skb;
> - continue;
> + goto cont;
>
> } else {
> last_lost = TCP_SKB_CB(skb)->end_seq;
> @@ -2268,7 +2317,7 @@ begin_fwd:
> }
>
> if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
> - continue;
> + goto cont;
>
> if (tcp_retransmit_skb(sk, skb))
> return;
> @@ -2278,6 +2327,9 @@ begin_fwd:
> inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
> inet_csk(sk)->icsk_rto,
> TCP_RTO_MAX);
> +cont:
> + skb = skb->next;
> + goto checknull;
> }
> }
>
--
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