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tcp: refine tcp_write_queue_empty() implementation

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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: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
This commit is contained in:
Eric Dumazet 2019-12-12 12:55:30 -08:00 • committed by Jakub Kicinski
parent 1f85e6267c
commit ee2aabd3fc
2 changed files with 13 additions and 3 deletions
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11
include/net/tcp.h
View file

@ -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); 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) 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) static inline bool tcp_rtx_queue_empty(const struct sock *sk)

5
net/ipv4/tcp_output.c
View file

@ -3129,7 +3129,7 @@ void sk_forced_mem_schedule(struct sock *sk, int size)
*/ */
void tcp_send_fin(struct sock *sk) 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); struct tcp_sock *tp = tcp_sk(sk);
/* Optimization, tack on the FIN if we have one skb in write queue and /* 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, * Note: in the latter case, FIN packet will be sent after a timeout,
* as TCP stack thinks it has already been transmitted. * as TCP stack thinks it has already been transmitted.
*/ */
tskb = tail;
if (!tskb && tcp_under_memory_pressure(sk)) if (!tskb && tcp_under_memory_pressure(sk))
tskb = skb_rb_last(&sk->tcp_rtx_queue); 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)->tcp_flags |= TCPHDR_FIN;
TCP_SKB_CB(tskb)->end_seq++; TCP_SKB_CB(tskb)->end_seq++;
tp->write_seq++; tp->write_seq++;
if (tcp_write_queue_empty(sk)) { if (!tail) {
/* This means tskb was already sent. /* This means tskb was already sent.
* Pretend we included the FIN on previous transmit. * Pretend we included the FIN on previous transmit.
* We need to set tp->snd_nxt to the value it would have * We need to set tp->snd_nxt to the value it would have