netdev - [PATCH net-next 05/19] ipmr: do not acquire mrt_lock in __pim

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Message-Id: <20220622051255.700309-6-edumazet@google.com>
Date:   Wed, 22 Jun 2022 05:12:41 +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>
Subject: [PATCH net-next 05/19] ipmr: do not acquire mrt_lock in __pim_rcv()

rcu_read_lock() protection is more than enough.

vif_dev_read() supports either mrt_lock or rcu_read_lock().

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv4/ipmr.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 8fe7a688cf41deeb99c7ca554f1788a956d2fdb9..8a94f9a459cd077d74b5e38c3d2f248620d4ecfc 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -582,6 +582,7 @@ static int __pim_rcv(struct mr_table *mrt, struct sk_buff *skb,
 {
 	struct net_device *reg_dev = NULL;
 	struct iphdr *encap;
+	int vif_num;
 
 	encap = (struct iphdr *)(skb_transport_header(skb) + pimlen);
 	/* Check that:
@@ -594,11 +595,10 @@ static int __pim_rcv(struct mr_table *mrt, struct sk_buff *skb,
 	    ntohs(encap->tot_len) + pimlen > skb->len)
 		return 1;
 
-	read_lock(&mrt_lock);
-	if (mrt->mroute_reg_vif_num >= 0)
-		reg_dev = vif_dev_read(&mrt->vif_table[mrt->mroute_reg_vif_num]);
-	read_unlock(&mrt_lock);
-
+	/* Pairs with WRITE_ONCE() in vif_add()/vid_delete() */
+	vif_num = READ_ONCE(mrt->mroute_reg_vif_num);
+	if (vif_num >= 0)
+		reg_dev = vif_dev_read(&mrt->vif_table[vif_num]);
 	if (!reg_dev)
 		return 1;
 
-- 
2.37.0.rc0.104.g0611611a94-goog