Commit ee2aabd3 authored by Eric Dumazet's avatar Eric Dumazet Committed by Jakub Kicinski
Browse files

tcp: refine tcp_write_queue_empty() implementation 



Due to how tcp_sendmsg() is implemented, we can have an empty
skb at the tail of the write queue.

Most [1] tcp_write_queue_empty() callers want to know if there is
anything to send (payload and/or FIN)

Instead of checking if the sk_write_queue is empty, we need
to test if tp->write_seq == tp->snd_nxt

[1] tcp_send_fin() was the only caller that expected to
 see if an skb was in the write queue, I have changed the code
 to reuse the tcp_write_queue_tail() result.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Acked-by: default avatarSoheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: default avatarJakub Kicinski <jakub.kicinski@netronome.com>
parent 1f85e626

include/net/tcp.h

+10 −1
Original line number Diff line number Diff line
@@ -1766,9 +1766,18 @@ static inline bool tcp_skb_is_last(const struct sock *sk, 
	return skb_queue_is_last(&sk->sk_write_queue, skb);

}



/**

 * tcp_write_queue_empty - test if any payload (or FIN) is available in write queue

 * @sk: socket

 *

 * Since the write queue can have a temporary empty skb in it,

 * we must not use "return skb_queue_empty(&sk->sk_write_queue)"

 */

static inline bool tcp_write_queue_empty(const struct sock *sk)

{

	return skb_queue_empty(&sk->sk_write_queue);

	const struct tcp_sock *tp = tcp_sk(sk);



	return tp->write_seq == tp->snd_nxt;

}



static inline bool tcp_rtx_queue_empty(const struct sock *sk)

net/ipv4/tcp_output.c

+3 −2
Original line number Diff line number Diff line
@@ -3129,7 +3129,7 @@ void sk_forced_mem_schedule(struct sock *sk, int size) 
 */

void tcp_send_fin(struct sock *sk)

{

	struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk);

	struct sk_buff *skb, *tskb, *tail = tcp_write_queue_tail(sk);

	struct tcp_sock *tp = tcp_sk(sk);



	/* Optimization, tack on the FIN if we have one skb in write queue and
@@ -3137,6 +3137,7 @@ void tcp_send_fin(struct sock *sk) 
	 * Note: in the latter case, FIN packet will be sent after a timeout,

	 * as TCP stack thinks it has already been transmitted.

	 */

	tskb = tail;

	if (!tskb && tcp_under_memory_pressure(sk))

		tskb = skb_rb_last(&sk->tcp_rtx_queue);
@@ -3144,7 +3145,7 @@ void tcp_send_fin(struct sock *sk) 
		TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;

		TCP_SKB_CB(tskb)->end_seq++;

		tp->write_seq++;

		if (tcp_write_queue_empty(sk)) {

		if (!tail) {

			/* This means tskb was already sent.

			 * Pretend we included the FIN on previous transmit.

			 * We need to set tp->snd_nxt to the value it would have

CRA Git | Maintained and supported by SUSTech CRA and CCSE