tcp: Fix a data-race around sysctl_tcp_early_retrans.

stable inclusion
from stable-v5.10.134
commit 11e8b013d16e5db63f8f76acceb5b86964098aaa
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5ZVR7

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=11e8b013d16e5db63f8f76acceb5b86964098aaa

--------------------------------

[ Upstream commit 52e65865 ]

While reading sysctl_tcp_early_retrans, it can be changed concurrently.
Thus, we need to add READ_ONCE() to its reader.

Fixes: eed530b6 ("tcp: early retransmit")
Signed-off-by: NKuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>

net/ipv4/tcp_output.c

@@ -2787,7 +2787,7 @@ bool tcp_schedule_loss_probe(struct sock *sk, bool advancing_rto)
 	if (rcu_access_pointer(tp->fastopen_rsk))
 		return false;
 
-	early_retrans = sock_net(sk)->ipv4.sysctl_tcp_early_retrans;
+	early_retrans = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_early_retrans);
 	/* Schedule a loss probe in 2*RTT for SACK capable connections
 	 * not in loss recovery, that are either limited by cwnd or application.
 	 */