Re: select()/socket has problems under 2.2.x.

Andrea Arcangeli (andrea@e-mind.com)
Fri, 5 Mar 1999 20:46:51 +0100 (CET)

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On Fri, 5 Mar 1999, Frederick (Rick) A Niles wrote:

>Andrea's patch only seemed to make the problem twice as bad. :)

I know it was bogus and was only a late-night (to tired to really
think at what was doing ;) guess.

Please apply this patch and you'll get the thing fixed. The thing was
completly select unrelated. It was the receiver that wasn't able to queue
incoming data. It wasn't able to read packets from the network due a
rcvbuf < of the truesize of the skbuff.

Here a snapshot of my fix (the diff is against 2.2.2_arca8.gz) just to
show to DaveM the interesting changes I did to fix the bug (but it will
not apply cleanly to 2.2.2 so apply the second down instead):

And here down the patch I ask you to try out and confirm that fix
everything for you. This second my patch is against clean 2.2.2 and it's
the diff between my current tree and 2.2.2. It includes also DaveM
Solaris-workaround:

Index: tcp_input.c
===================================================================
RCS file: /var/cvs/linux/net/ipv4/tcp_input.c,v
retrieving revision 1.1.1.6
diff -u -r1.1.1.6 tcp_input.c
--- tcp_input.c 1999/02/23 16:48:26 1.1.1.6
+++ linux/net/ipv4/tcp_input.c 1999/03/05 19:44:30
@@ -55,6 +55,13 @@
* work without delayed acks.
* Andi Kleen: Process packets with PSH set in the
* fast path.
+ * Andrea Arcangeli: TCP_NODELAY disable delacks.
+ * Andrea Arcangeli: Delay also the first ack to be able to
+ * join the ack in the first data packet.
+ * Andrea Arcangeli: Always queue a packet from the other
+ * end if all receive queues are empty,
+ * this avoid the receiver to deadlock
+ * if rcvbuf < packet truesize.
*/

#include <linux/config.h>
@@ -99,12 +106,11 @@
if(tp->ato == 0) {
tp->lrcvtime = jiffies;

- /* Help sender leave slow start quickly,
- * and also makes sure we do not take this
- * branch ever again for this connection.
+ /*
+ * Don't enter quickack mode to be able to join the first
+ * ack with a data packet. -arca
*/
- tp->ato = 1;
- tcp_enter_quickack_mode(tp);
+ tp->ato = (HZ+49)/50;
} else {
int m = jiffies - tp->lrcvtime;

@@ -135,9 +141,9 @@
*/
if(th->psh && (skb->len < (tp->mss_cache >> 1))) {
/* Preserve the quickack state. */
- if((tp->ato & 0x7fffffff) > HZ/50)
+ if((tp->ato & 0x7fffffff) > (HZ+49)/50)
tp->ato = ((tp->ato & 0x80000000) |
- (HZ/50));
+ ((HZ+49)/50));
}
}

@@ -241,7 +247,7 @@
extern __inline__ int tcp_paws_discard(struct tcp_opt *tp, struct tcphdr *th, unsigned len)
{
/* ts_recent must be younger than 24 days */
- return (((jiffies - tp->ts_recent_stamp) >= PAWS_24DAYS) ||
+ return (((s32)(jiffies - tp->ts_recent_stamp) >= PAWS_24DAYS) ||
(((s32)(tp->rcv_tsval-tp->ts_recent) < 0) &&
/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM */
(len != (th->doff * 4))));
@@ -1484,7 +1490,8 @@
* Make sure to do this before moving snd_nxt, otherwise
* data might be acked for that we don't have enough room.
*/
- if (atomic_read(&sk->rmem_alloc) > sk->rcvbuf) {
+ if (!sock_rspace(sk) && (skb_queue_len(&sk->receive_queue) ||
+ skb_queue_len(&tp->out_of_order_queue))) {
if (prune_queue(sk) < 0) {
/* Still not enough room. That can happen when
* skb->true_size differs significantly from skb->len.
@@ -1580,7 +1587,9 @@
/* We entered "quick ACK" mode or... */
tcp_in_quickack_mode(tp) ||
/* We have out of order data */
- (skb_peek(&tp->out_of_order_queue) != NULL)) {
+ (skb_peek(&tp->out_of_order_queue) != NULL) ||
+ /* TCP_NODELAY is set */
+ sk->nonagle == 1) {
/* Then ack it now */
tcp_send_ack(sk);
} else {
@@ -1821,7 +1830,9 @@
goto discard;
}
} else if (TCP_SKB_CB(skb)->ack_seq == tp->snd_una &&
- atomic_read(&sk->rmem_alloc) <= sk->rcvbuf) {
+ (sock_rspace(sk) ||
+ (!skb_queue_len(&sk->receive_queue) &&
+ !skb_queue_len(&tp->out_of_order_queue)))) {
/* Bulk data transfer: receiver */
__skb_pull(skb,th->doff*4);

Index: tcp_output.c
===================================================================
RCS file: /var/cvs/linux/net/ipv4/tcp_output.c,v
retrieving revision 1.1.1.5
diff -u -r1.1.1.5 tcp_output.c
--- tcp_output.c 1999/02/23 16:48:26 1.1.1.5
+++ linux/net/ipv4/tcp_output.c 1999/03/02 16:53:50
@@ -580,6 +580,19 @@
if(tp->af_specific->rebuild_header(sk))
return 1; /* Routing failure or similar. */

+ /* Solaris sucks. */
+ if(skb->len > 0 &&
+ (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) &&
+ tp->snd_una == (TCP_SKB_CB(skb)->end_seq - 1)) {
+#if 1
+ printk("TCP: Doing Solaris hack for [%p:%08x:%04x:%08x]\n",
+ skb, sk->daddr, sk->dport, tp->snd_una);
+#endif
+ TCP_SKB_CB(skb)->seq = TCP_SKB_CB(skb)->end_seq - 1;
+ skb_trim(skb, 0);
+ skb->csum = 0;
+ }
+
/* Ok, we're gonna send it out, update state. */
TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_RETRANS;
tp->retrans_out++;
@@ -973,6 +986,8 @@
timeout = tp->ato;
if (timeout > max_timeout)
timeout = max_timeout;
+ if (timeout < (HZ+49)/50)
+ timeout = (HZ+49)/50;
timeout += jiffies;

/* Use new timeout only if there wasn't a older one earlier. */
@@ -980,7 +995,7 @@
tp->delack_timer.expires = timeout;
add_timer(&tp->delack_timer);
} else {
- if (timeout < tp->delack_timer.expires)
+ if (time_before(timeout, tp->delack_timer.expires))
mod_timer(&tp->delack_timer, timeout);
}
}

Comments?

Andrea Arcangeli

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