On Thu, 29 Mar 2007, Andrew Morton wrote: > Full -mm lineup. The x86_64 box was acting as a distcc server at the time. > > Nothing hit the logs, I'm afraid. But almost all the info is in > http://userweb.kernel.org/~akpm/s5000494.jpg > > <pokes around in gdb a bit> > > It died in tcp_update_scoreboard_fack() here: > > if ((!IsFack(tp) || !tcp_skb_timedout(sk, skb)) && > after(TCP_SKB_CB(skb)->seq, tp->high_seq)) { > /* RFC: should we have find_below? */ > skb = tcp_write_queue_find(sk, tp->high_seq); > not_marked_skb = skb; > skb = tcp_write_queue_prev(sk, skb); > /* Timedout top is again uncertain? */ > if (tcp_skb_timedout(sk, skb)) > timedout_continue = 1; > } > > > (gdb) l *0xffffffff8048ded8 > 0xffffffff8048ded8 is in tcp_update_scoreboard_fack (include/net/tcp.h:1197). > 1192 return skb->next; > 1193 } > 1194 > 1195 static inline struct sk_buff *tcp_write_queue_prev(struct sock *sk, > struct sk_buff *skb) > 1196 { > 1197 return skb->prev; > 1198 } > 1199 > 1200 #define tcp_for_write_queue(skb, sk) > \ > > (gdb) x/10i 0xffffffff8048ded8 > 0xffffffff8048ded8 <tcp_update_scoreboard_fack+528>: mov 0x8(%rdx),%r12 > > So if that "CR2: 0000000000000008" is the access address then it appears that > `skb' is NULL. tcp_write_queue_find() didn't find nuthin.
If there is nothing at high_seq (application hasn't given any data to/past that point), the search fails to find any skb and returns NULL... But I have no idea how this can happen? As TCP does after(skb->seq, tp->high_seq) (even in the quoted code block) guaranteeing that something is there after the high_seq for TCP to step temporarily on... So at least one skb should have it's end_seq after tp->high_seq (actually there should be at least two valid skbs after tp->high_seq since the used sequence number space does not have holes), which should be enough to get an existing skb from write_queue_find?! I also checked all call paths to tcp_update_scoreboard_fack to make sure that snd_una hasn't gone past high_seq and found nothing suspicious (and that wouldn't return NULL anyway I think)... -- i. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
