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Subject[PATCH RT 08/15] net: take the tcp_sk_lock lock with BH disabled
4.9.65-rt57-rc1 stable review patch.
If anyone has any objections, please let me know.

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

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Lockdep may complain about an unsafe locking scenario:
| CPU0 CPU1
| ---- ----
| lock((tcp_sk_lock).lock);
| lock(&per_cpu(local_softirq_locks[i], __cpu).lock);
| lock((tcp_sk_lock).lock);
| lock(&per_cpu(local_softirq_locks[i], __cpu).lock);

in the call paths:
do_current_softirqs -> tcp_v4_send_ack()
vs
tcp_v4_send_reset -> do_current_softirqs().

This should not happen since local_softirq_locks is per CPU. Reversing
the order makes lockdep happy.

Reported-by: Jacek Konieczny <jajcus@jajcus.net>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
net/ipv4/tcp_ipv4.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 3336e1534bc5..3b7298459c87 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -698,8 +698,8 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)

arg.tos = ip_hdr(skb)->tos;

- local_lock(tcp_sk_lock);
local_bh_disable();
+ local_lock(tcp_sk_lock);
ip_send_unicast_reply(*this_cpu_ptr(net->ipv4.tcp_sk),
skb, &TCP_SKB_CB(skb)->header.h4.opt,
ip_hdr(skb)->saddr, ip_hdr(skb)->daddr,
@@ -707,8 +707,8 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)

__TCP_INC_STATS(net, TCP_MIB_OUTSEGS);
__TCP_INC_STATS(net, TCP_MIB_OUTRSTS);
- local_bh_enable();
local_unlock(tcp_sk_lock);
+ local_bh_enable();

#ifdef CONFIG_TCP_MD5SIG
out:
@@ -784,16 +784,16 @@ static void tcp_v4_send_ack(struct net *net,
if (oif)
arg.bound_dev_if = oif;
arg.tos = tos;
- local_lock(tcp_sk_lock);
local_bh_disable();
+ local_lock(tcp_sk_lock);
ip_send_unicast_reply(*this_cpu_ptr(net->ipv4.tcp_sk),
skb, &TCP_SKB_CB(skb)->header.h4.opt,
ip_hdr(skb)->saddr, ip_hdr(skb)->daddr,
&arg, arg.iov[0].iov_len);

__TCP_INC_STATS(net, TCP_MIB_OUTSEGS);
- local_bh_enable();
local_unlock(tcp_sk_lock);
+ local_bh_enable();
}

static void tcp_v4_timewait_ack(struct sock *sk, struct sk_buff *skb)
--
2.13.2

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