[PATCH v3 6/8] tls: Flush backlog before tls_rx_rec_wait in read_sock

[Chuck Lever <cel@kernel.org>]

From: Chuck Lever <chuck.lever@oracle.com>

While lock_sock is held during read_sock, incoming TCP segments
land on sk->sk_backlog rather than sk->sk_receive_queue.
tls_rx_rec_wait() inspects only sk_receive_queue, so backlog
data remains invisible until release_sock() drains it, forcing
an extra workqueue cycle for records that arrive during
decryption.

Calling sk_flush_backlog() before tls_rx_rec_wait() moves
backlog data into sk_receive_queue, where tls_strp_check_rcv()
can parse it immediately. The existing tls_read_flush_backlog
call after decryption is retained for TCP window management.

Acked-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/tls/tls_sw.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index 43d37b0e6d59..7e1560d5ab79 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -2387,6 +2387,11 @@ int tls_sw_read_sock(struct sock *sk, read_descriptor_t *desc,
 		} else {
 			struct tls_decrypt_arg darg;
 
+			/* Drain backlog so segments that arrived while the
+			 * lock was held appear on sk_receive_queue before
+			 * tls_rx_rec_wait waits for a new record.
+			 */
+			sk_flush_backlog(sk);
 			err = tls_rx_rec_wait(sk, NULL, true, released);
 			if (err <= 0)
 				goto read_sock_end;
-- 
2.52.0