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tcp: Deal with DSACKs, and adjust rescue hole on success.

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When a rescue retransmission is successful, rather than
inserting new holes to the left of it, adjust the old
rescue entry to cover the missed sequence space.

Also, as snd_fack may be stale by that point, pull it forward
in order to never create a hole left of snd_una/th_ack.

Finally, with DSACKs, tcp_sack_doack() may be called
with new full ACKs but a DSACK block. Account for this
eventuality properly to keep sacked_bytes >= 0.

MFC after: 3 days
Reviewed By: kbowling, tuexen, #transport
Sponsored by: NetApp, Inc.
Differential Revision: https://reviews.freebsd.org/D29835
This commit is contained in:
Richard Scheffenegger 2021-04-20 14:53:56 +02:00
parent 9ca874cf74
commit a649f1f6fd
1 changed files with 47 additions and 29 deletions
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76
sys/netinet/tcp_sack.c
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@ -497,7 +497,7 @@ static struct sackhole *
tcp_sackhole_insert(struct tcpcb *tp, tcp_seq start, tcp_seq end,
struct sackhole *after)
{
struct sackhole *hole, *tail;
struct sackhole *hole;
/* Allocate a new SACK hole. */
hole = tcp_sackhole_alloc(tp, start, end);
@ -508,15 +508,7 @@ tcp_sackhole_insert(struct tcpcb *tp, tcp_seq start, tcp_seq end,
if (after != NULL)
TAILQ_INSERT_AFTER(&tp->snd_holes, after, hole, scblink);
else
/*
* With Rescue Retransmission, new holes may need to
* be inserted just before the tail.
*/
if (((tail = TAILQ_LAST_FAST(&tp->snd_holes, sackhole,
scblink)) != NULL) && SEQ_LEQ(end, tail->start))
TAILQ_INSERT_BEFORE(tail, hole, scblink);
else
TAILQ_INSERT_TAIL(&tp->snd_holes, hole, scblink);
TAILQ_INSERT_TAIL(&tp->snd_holes, hole, scblink);
/* Update SACK hint. */
if (tp->sackhint.nexthole == NULL)
@ -573,6 +565,15 @@ tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack)
left_edge_delta = th_ack - tp->snd_una;
sack_blocks[num_sack_blks].start = tp->snd_una;
sack_blocks[num_sack_blks++].end = th_ack;
/*
* Pulling snd_fack forward if we got here
* due to DSACK blocks
*/
if (SEQ_LT(tp->snd_fack, th_ack)) {
delivered_data += th_ack - tp->snd_una;
tp->snd_fack = th_ack;
sack_changed = 1;
}
}
/*
* Append received valid SACK blocks to sack_blocks[], but only if we
@ -642,35 +643,52 @@ tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack)
tp->sackhint.last_sack_ack = sblkp->end;
if (SEQ_LT(tp->snd_fack, sblkp->start)) {
/*
* The highest SACK block is beyond fack. Append new SACK
* hole at the tail. If the second or later highest SACK
* blocks are also beyond the current fack, they will be
* inserted by way of hole splitting in the while-loop below.
* The highest SACK block is beyond fack. First,
* check if there was a successful Rescue Retransmission,
* and move this hole left. With normal holes, snd_fack
* is always to the right of the end.
*/
temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL);
if (temp != NULL) {
if (((temp = TAILQ_LAST(&tp->snd_holes, sackhole_head)) != NULL) &&
SEQ_LEQ(tp->snd_fack,temp->end)) {
temp->start = SEQ_MAX(tp->snd_fack, SEQ_MAX(tp->snd_una, th_ack));
temp->end = sblkp->start;
temp->rxmit = temp->start;
delivered_data += sblkp->end - sblkp->start;
tp->snd_fack = sblkp->end;
/* Go to the previous sack block. */
sblkp--;
sack_changed = 1;
} else {
/*
* We failed to add a new hole based on the current
* sack block. Skip over all the sack blocks that
* fall completely to the right of snd_fack and
* proceed to trim the scoreboard based on the
* remaining sack blocks. This also trims the
* scoreboard for th_ack (which is sack_blocks[0]).
* Append a new SACK hole at the tail. If the
* second or later highest SACK blocks are also
* beyond the current fack, they will be inserted
* by way of hole splitting in the while-loop below.
*/
while (sblkp >= sack_blocks &&
SEQ_LT(tp->snd_fack, sblkp->start))
sblkp--;
if (sblkp >= sack_blocks &&
SEQ_LT(tp->snd_fack, sblkp->end)) {
delivered_data += sblkp->end - tp->snd_fack;
temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL);
if (temp != NULL) {
delivered_data += sblkp->end - sblkp->start;
tp->snd_fack = sblkp->end;
/* Go to the previous sack block. */
sblkp--;
sack_changed = 1;
} else {
/*
* We failed to add a new hole based on the current
* sack block. Skip over all the sack blocks that
* fall completely to the right of snd_fack and
* proceed to trim the scoreboard based on the
* remaining sack blocks. This also trims the
* scoreboard for th_ack (which is sack_blocks[0]).
*/
while (sblkp >= sack_blocks &&
SEQ_LT(tp->snd_fack, sblkp->start))
sblkp--;
if (sblkp >= sack_blocks &&
SEQ_LT(tp->snd_fack, sblkp->end)) {
delivered_data += sblkp->end - tp->snd_fack;
tp->snd_fack = sblkp->end;
sack_changed = 1;
}
}
}
} else if (SEQ_LT(tp->snd_fack, sblkp->end)) {