diff mbox series

[net,3/3] tcp: fix TFO SYN_RECV to not zero retrans_stamp with retransmits out

Message ID 20241001200517.2756803-4-ncardwell.sw@gmail.com (mailing list archive)
State Accepted
Commit 27c80efcc20486c82698f05f00e288b44513c86b
Delegated to: Netdev Maintainers
Headers show
Series tcp: 3 fixes for retrans_stamp and undo logic | expand

Checks

Context Check Description
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for net
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag present in non-next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 9 this patch: 9
netdev/build_tools success No tools touched, skip
netdev/cc_maintainers warning 2 maintainers not CCed: pabeni@redhat.com dsahern@kernel.org
netdev/build_clang success Errors and warnings before: 9 this patch: 9
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 Fixes tag looks correct
netdev/build_allmodconfig_warn fail Errors and warnings before: 12 this patch: 12
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 19 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 0 now: 0

Commit Message

Neal Cardwell Oct. 1, 2024, 8:05 p.m. UTC 
From: Neal Cardwell <ncardwell@google.com>

Fix tcp_rcv_synrecv_state_fastopen() to not zero retrans_stamp
if retransmits are outstanding.

tcp_fastopen_synack_timer() sets retrans_stamp, so typically we'll
need to zero retrans_stamp here to prevent spurious
retransmits_timed_out(). The logic to zero retrans_stamp is from this
2019 commit:

commit cd736d8b67fb ("tcp: fix retrans timestamp on passive Fast Open")

However, in the corner case where the ACK of our TFO SYNACK carried
some SACK blocks that caused us to enter TCP_CA_Recovery then that
non-zero retrans_stamp corresponds to the active fast recovery, and we
need to leave retrans_stamp with its current non-zero value, for
correct ETIMEDOUT and undo behavior.

Fixes: cd736d8b67fb ("tcp: fix retrans timestamp on passive Fast Open")
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/ipv4/tcp_input.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 774fe1de8a922..e7111cda25494 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6684,10 +6684,17 @@  static void tcp_rcv_synrecv_state_fastopen(struct sock *sk)
 	if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss && !tp->packets_out)
 		tcp_try_undo_recovery(sk);
 
-	/* Reset rtx states to prevent spurious retransmits_timed_out() */
 	tcp_update_rto_time(tp);
-	tp->retrans_stamp = 0;
 	inet_csk(sk)->icsk_retransmits = 0;
+	/* In tcp_fastopen_synack_timer() on the first SYNACK RTO we set
+	 * retrans_stamp but don't enter CA_Loss, so in case that happened we
+	 * need to zero retrans_stamp here to prevent spurious
+	 * retransmits_timed_out(). However, if the ACK of our SYNACK caused us
+	 * to enter CA_Recovery then we need to leave retrans_stamp as it was
+	 * set entering CA_Recovery, for correct retransmits_timed_out() and
+	 * undo behavior.
+	 */
+	tcp_retrans_stamp_cleanup(sk);
 
 	/* Once we leave TCP_SYN_RECV or TCP_FIN_WAIT_1,
 	 * we no longer need req so release it.