[PATCH net-next v3 1/5] net: Revert "ipv4: get rid of ip_ra_lock"

[Kirill Tkhai]

This reverts commit ba3f571d5dde. The commit was made
after 1215e51edad1 "ipv4: fix a deadlock in ip_ra_control",
and killed ip_ra_lock, which became useless after rtnl_lock()
made used to destroy every raw ipv4 socket. This scales
very bad, and next patch in series reverts 1215e51edad1.
ip_ra_lock will be used again.

Signed-off-by: Kirill Tkhai <ktk...@virtuozzo.com>
---
 net/ipv4/ip_sockglue.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 74c962b9b09c..be7c3b71914d 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -334,6 +334,7 @@ int ip_cmsg_send(struct sock *sk, struct msghdr *msg, 
struct ipcm_cookie *ipc,
    sent to multicast group to reach destination designated router.
  */
 struct ip_ra_chain __rcu *ip_ra_chain;
+static DEFINE_SPINLOCK(ip_ra_lock);
 
 
 static void ip_ra_destroy_rcu(struct rcu_head *head)
@@ -355,17 +356,21 @@ int ip_ra_control(struct sock *sk, unsigned char on,
 
        new_ra = on ? kmalloc(sizeof(*new_ra), GFP_KERNEL) : NULL;
 
+       spin_lock_bh(&ip_ra_lock);
        for (rap = &ip_ra_chain;
-            (ra = rtnl_dereference(*rap)) != NULL;
+            (ra = rcu_dereference_protected(*rap,
+                       lockdep_is_held(&ip_ra_lock))) != NULL;
             rap = &ra->next) {
                if (ra->sk == sk) {
                        if (on) {
+                               spin_unlock_bh(&ip_ra_lock);
                                kfree(new_ra);
                                return -EADDRINUSE;
                        }
                        /* dont let ip_call_ra_chain() use sk again */
                        ra->sk = NULL;
                        RCU_INIT_POINTER(*rap, ra->next);
+                       spin_unlock_bh(&ip_ra_lock);
 
                        if (ra->destructor)
                                ra->destructor(sk);
@@ -379,14 +384,17 @@ int ip_ra_control(struct sock *sk, unsigned char on,
                        return 0;
                }
        }
-       if (!new_ra)
+       if (!new_ra) {
+               spin_unlock_bh(&ip_ra_lock);
                return -ENOBUFS;
+       }
        new_ra->sk = sk;
        new_ra->destructor = destructor;
 
        RCU_INIT_POINTER(new_ra->next, ra);
        rcu_assign_pointer(*rap, new_ra);
        sock_hold(sk);
+       spin_unlock_bh(&ip_ra_lock);
 
        return 0;
 }