Messages in this thread | | | Subject | Re: oops in tcp_xmit_retransmit_queue() w/ v2.6.32.15 | From | Eric Dumazet <> | Date | Sun, 11 Jul 2010 19:46:22 +0200 |
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Le dimanche 11 juillet 2010 à 19:06 +0200, Eric Dumazet a écrit : > Le dimanche 11 juillet 2010 à 19:09 +0300, Ilpo Järvinen a écrit : > > On Thu, 8 Jul 2010, Tejun Heo wrote: > > > > > We've been seeing oops in tcp_xmit_retransmit_queue() w/ 2.6.32.15. > > > Please see the attached photoshoot. This is happening on a HPC > > > cluster and very interestingly caused by one particular job. How long > > > it takes isn't clear yet (at least more than a day) but when it > > > happens it happens on a lot of machines in relatively short time. > > > > > > With a bit of disassemblying, I've found that the oops is happening > > > during tcp_for_write_queue_from() because the skb->next points to > > > NULL. > > > > > > void tcp_xmit_retransmit_queue(struct sock *sk) > > > { > > > ... > > > if (tp->retransmit_skb_hint) { > > > skb = tp->retransmit_skb_hint; > > > last_lost = TCP_SKB_CB(skb)->end_seq; > > > if (after(last_lost, tp->retransmit_high)) > > > last_lost = tp->retransmit_high; > > > } else { > > > skb = tcp_write_queue_head(sk); > > > last_lost = tp->snd_una; > > > } > > > > > > => tcp_for_write_queue_from(skb, sk) { > > > __u8 sacked = TCP_SKB_CB(skb)->sacked; > > > > > > if (skb == tcp_send_head(sk)) > > > break; > > > /* we could do better than to assign each time */ > > > if (hole == NULL) > > > > > > This can happen for one of the following reasons, > > > > > > 1. tp->retransmit_skb_hint is NULL and tcp_write_queue_head() is NULL > > > too. ie. tcp_xmit_retransmit_queue() is called on an empty write > > > queue for some reason. > > > > > > 2. tp->retransmit_skb_hint is pointing to a skb which is not on the > > > write_queue. ie. somebody forgot to update hint while removing the > > > skb from the write queue. > > > > Once again I've read the unlinkers through, and only thing that could > > cause this is tcp_send_synack (others do deal with the hints) but I think > > Eric already proposed a patch to that but we never got anywhere due to > > some counterargument why it wouldn't take place (too far away for me to > > remember, see archives about the discussions). ...But if you want be dead > > sure some WARN_ON there might not hurt. Also the purging of the whole > > queue was a similar suspect I then came across (but that would only > > materialize with sk reuse happening e.g., with nfs which the other guys > > weren't using). > > > > Hmm. > > This sounds familiar to me, but I cannot remember the discussion you > mention or the patch. > > Or maybe it was the TCP transaction thing ? (including data in SYN or > SYN-ACK packet)
Hmm, I cannot find where we reset restransmit_skb_hint in tcp_mtu_probe(), if we call tcp_unlink_write_queue().
if (skb->len <= copy) { /* We've eaten all the data from this skb. * Throw it away. */ TCP_SKB_CB(nskb)->flags |= TCP_SKB_CB(skb)->flags; <<>> tcp_unlink_write_queue(skb, sk); sk_wmem_free_skb(sk, skb); } else {
Sorry if this was already discussed. We might add a comment here in anycase ;)
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