netdev - [PATCH net] tcp: tcp_check_req() can be called from process context

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Date:   Mon, 27 Feb 2023 08:33:36 +0000
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        Eric Dumazet <edumazet@...gle.com>,
        Frederick Lawler <fred@...udflare.com>
Subject: [PATCH net] tcp: tcp_check_req() can be called from process context

This is a follow up of commit 0a375c822497 ("tcp: tcp_rtx_synack()
can be called from process context").

Frederick Lawler reported another "__this_cpu_add() in preemptible"
warning caused by the same reason.

In my former patch I took care of tcp_rtx_synack()
but forgot that tcp_check_req() also contained some SNMP updates.

Note that some parts of tcp_check_req() always run in BH context,
I added a comment to clarify this.

Fixes: 8336886f786f ("tcp: TCP Fast Open Server - support TFO listeners")
Link: https://lore.kernel.org/netdev/8cd33923-a21d-397c-e46b-2a068c287b03@cloudflare.com/T/
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: Frederick Lawler <fred@...udflare.com>
Tested-by: Frederick Lawler <fred@...udflare.com>
---
 net/ipv4/tcp_minisocks.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index e002f2e1d4f2de0397f2cc7ec0a14a05efbd802b..9a7ef7732c24c94d4a01d5911ebe51f21371a457 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -597,6 +597,9 @@ EXPORT_SYMBOL(tcp_create_openreq_child);
  * validation and inside tcp_v4_reqsk_send_ack(). Can we do better?
  *
  * We don't need to initialize tmp_opt.sack_ok as we don't use the results
+ *
+ * Note: If @fastopen is true, this can be called from process context.
+ *       Otherwise, this is from BH context.
  */
 
 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
@@ -748,7 +751,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 					  &tcp_rsk(req)->last_oow_ack_time))
 			req->rsk_ops->send_ack(sk, skb, req);
 		if (paws_reject)
-			__NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
+			NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
 		return NULL;
 	}
 
@@ -767,7 +770,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 	 *	   "fourth, check the SYN bit"
 	 */
 	if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
-		__TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
+		TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
 		goto embryonic_reset;
 	}
 
-- 
2.39.2.637.g21b0678d19-goog