netdev - [PATCH net-next 11/19] ip6mr: do not acquire mrt_lock in pim6

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Message-Id: <20220622051255.700309-12-edumazet@google.com>
Date:   Wed, 22 Jun 2022 05:12:47 +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 11/19] ip6mr: do not acquire mrt_lock in pim6_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/ipv6/ip6mr.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index a6d97952bf5306c245996c612107d0c851bbc822..fa6720377e82d732ccafa02b37cc28e0ab1cea07 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -559,12 +559,11 @@ static int pim6_rcv(struct sk_buff *skb)
 
 	if (ip6mr_fib_lookup(net, &fl6, &mrt) < 0)
 		goto drop;
-	reg_vif_num = mrt->mroute_reg_vif_num;
 
-	read_lock(&mrt_lock);
+	/* Pairs with WRITE_ONCE() in mif6_add()/mif6_delete() */
+	reg_vif_num = READ_ONCE(mrt->mroute_reg_vif_num);
 	if (reg_vif_num >= 0)
 		reg_dev = vif_dev_read(&mrt->vif_table[reg_vif_num]);
-	read_unlock(&mrt_lock);
 
 	if (!reg_dev)
 		goto drop;
-- 
2.37.0.rc0.104.g0611611a94-goog