diff mbox series

[net-next,1/3] tcp: remove dubious FIN exception from tcp_cwnd_test()

Message ID 20240418214600.1291486-2-edumazet@google.com (mailing list archive)
State Accepted
Commit 22555032c513e62fe744d4cdd553539897e8e922
Delegated to: Netdev Maintainers
Headers show
Series tcp: avoid sending too small packets | expand

Checks

Context Check Description
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for net-next
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 928 this patch: 928
netdev/build_tools success No tools touched, skip
netdev/cc_maintainers warning 1 maintainers not CCed: dsahern@kernel.org
netdev/build_clang success Errors and warnings before: 940 this patch: 940
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 939 this patch: 939
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 47 lines checked
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 1 this patch: 1
netdev/source_inline success Was 1 now: 0
netdev/contest success net-next-2024-04-21--03-00 (tests: 995)

Commit Message

Eric Dumazet April 18, 2024, 9:45 p.m. UTC
tcp_cwnd_test() has a special handing for the last packet in
the write queue if it is smaller than one MSS and has the FIN flag.

This is in violation of TCP RFC, and seems quite dubious.

This packet can be sent only if the current CWND is bigger
than the number of packets in flight.

Making tcp_cwnd_test() result independent of the first skb
in the write queue is needed for the last patch of the series.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/ipv4/tcp_output.c | 18 +++++-------------
 1 file changed, 5 insertions(+), 13 deletions(-)
diff mbox series

Patch

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 61119d42b0fd27a3736e136b1e81f6fc2d4cb44b..acbc76ca3e640354880c62c2423cfe4ba99f0be3 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2073,16 +2073,10 @@  static unsigned int tcp_mss_split_point(const struct sock *sk,
 /* Can at least one segment of SKB be sent right now, according to the
  * congestion window rules?  If so, return how many segments are allowed.
  */
-static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
-					 const struct sk_buff *skb)
+static u32 tcp_cwnd_test(const struct tcp_sock *tp)
 {
 	u32 in_flight, cwnd, halfcwnd;
 
-	/* Don't be strict about the congestion window for the final FIN.  */
-	if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
-	    tcp_skb_pcount(skb) == 1)
-		return 1;
-
 	in_flight = tcp_packets_in_flight(tp);
 	cwnd = tcp_snd_cwnd(tp);
 	if (in_flight >= cwnd)
@@ -2706,10 +2700,9 @@  static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct sk_buff *skb;
 	unsigned int tso_segs, sent_pkts;
-	int cwnd_quota;
+	u32 cwnd_quota, max_segs;
 	int result;
 	bool is_cwnd_limited = false, is_rwnd_limited = false;
-	u32 max_segs;
 
 	sent_pkts = 0;
 
@@ -2743,7 +2736,7 @@  static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
 		tso_segs = tcp_init_tso_segs(skb, mss_now);
 		BUG_ON(!tso_segs);
 
-		cwnd_quota = tcp_cwnd_test(tp, skb);
+		cwnd_quota = tcp_cwnd_test(tp);
 		if (!cwnd_quota) {
 			if (push_one == 2)
 				/* Force out a loss probe pkt. */
@@ -2772,9 +2765,8 @@  static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
 		limit = mss_now;
 		if (tso_segs > 1 && !tcp_urg_mode(tp))
 			limit = tcp_mss_split_point(sk, skb, mss_now,
-						    min_t(unsigned int,
-							  cwnd_quota,
-							  max_segs),
+						    min(cwnd_quota,
+							max_segs),
 						    nonagle);
 
 		if (skb->len > limit &&