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@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 8fe7a68..8a94f9a 100644 (file)
--- 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;