net: Fix a data-race around sysctl_net_busy_read.

stable inclusion
from stable-v5.10.140
commit 410c88314ce351c9c77ec68da1d37bd91ddd76a2
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I63FTT

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=410c88314ce351c9c77ec68da1d37bd91ddd76a2

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

[ Upstream commit e59ef36f ]

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

Fixes: 2d48d67f ("net: poll/select low latency socket support")
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/core/sock.c

@@ -3031,7 +3031,7 @@ void sock_init_data(struct socket *sock, struct sock *sk)
 
 #ifdef CONFIG_NET_RX_BUSY_POLL
 	sk->sk_napi_id		=	0;
-	sk->sk_ll_usec		=	sysctl_net_busy_read;
+	sk->sk_ll_usec		=	READ_ONCE(sysctl_net_busy_read);
 #endif
 
 	sk->sk_max_pacing_rate = ~0UL;