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tcp: bug #50614: move unsent queue check/pcb->snd_buf update

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This commit corrects what looks like an ancient incorrect organization
of the logic for processing an ACK which acks new data.  Once moved,
we can also change to using TCP_SEQ_LEQ on ackno instead of TCP_BETWEEN
because ackno has already been checked against snd_nxt

The work of checking the unsent queue and updating pcb->snd_buf (both
steps required for new data ACK) should be located under the conditional
that checks TCP_SEQ_BETWEEN(ackno, pcb->lastack+1, pcb->snd_nxt)

The comment following the unsent queue check/pcb->snd_buf update even
indicates "End of ACK for new data processing" when the logic is clearly
outside of this check

From what I can tell, this mis-organization isn't causing any incorrect
behavior since the unsent queue checked that ackno was between start of
segment and snd_nxt and recv_acked would be 0 during pcb->snd_buf update.
Instead this is waisted work for duplicate ACKS (can be common) and other
old ACKs
This commit is contained in:
Joel Cunningham 2017-03-22 16:19:23 -05:00
parent 720f9b3a0b
commit c722261142
1 changed files with 35 additions and 35 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
src/core/tcp_in.c
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@ -1188,10 +1188,6 @@ tcp_receive(struct tcp_pcb *pcb)
nd6_reachability_hint(ip6_current_src_addr());
}
#endif /* LWIP_IPV6 && LWIP_ND6_TCP_REACHABILITY_HINTS*/
} else {
/* Out of sequence ACK, didn't really ack anything */
tcp_send_empty_ack(pcb);
}
/* We go through the ->unsent list to see if any of the segments
on the list are acknowledged by the ACK. This may seem
@ -1200,8 +1196,8 @@ tcp_receive(struct tcp_pcb *pcb)
->unsent list after a retransmission, so these segments may
in fact have been sent once. */
while (pcb->unsent != NULL &&
TCP_SEQ_BETWEEN(ackno, lwip_ntohl(pcb->unsent->tcphdr->seqno) +
TCP_TCPLEN(pcb->unsent), pcb->snd_nxt)) {
TCP_SEQ_LEQ(lwip_ntohl(pcb->unsent->tcphdr->seqno) +
TCP_TCPLEN(pcb->unsent), ackno)) {
LWIP_DEBUGF(TCP_INPUT_DEBUG, ("tcp_receive: removing %"U32_F":%"U32_F" from pcb->unsent\n",
lwip_ntohl(pcb->unsent->tcphdr->seqno), lwip_ntohl(pcb->unsent->tcphdr->seqno) +
TCP_TCPLEN(pcb->unsent)));
@ -1227,6 +1223,10 @@ tcp_receive(struct tcp_pcb *pcb)
}
pcb->snd_buf += recv_acked;
/* End of ACK for new data processing. */
} else {
/* Out of sequence ACK, didn't really ack anything */
tcp_send_empty_ack(pcb);
}
LWIP_DEBUGF(TCP_RTO_DEBUG, ("tcp_receive: pcb->rttest %"U32_F" rtseq %"U32_F" ackno %"U32_F"\n",
pcb->rttest, pcb->rtseq, ackno));