ipv6: mcast: RCU conversion

ipv6_sk_mc_lock rwlock becomes a spinlock.

readers (inet6_mc_check()) now takes rcu_read_lock() instead of read
lock. Writers dont need to disable BH anymore.

struct ipv6_mc_socklist objects are reclaimed after one RCU grace
period.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 47 insertions, 33 deletions

diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 8e429d0e0405..0c997767429a 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -364,7 +364,7 @@ struct ipv6_pinfo {
 
         __u32                   dst_cookie;
 
-        struct ipv6_mc_socklist *ipv6_mc_list;
+        struct ipv6_mc_socklist __rcu *ipv6_mc_list;
         struct ipv6_ac_socklist *ipv6_ac_list;
         struct ipv6_fl_socklist *ipv6_fl_list;
 
diff --git a/include/net/if_inet6.h b/include/net/if_inet6.h
index f95ff8d9aa47..04977eefb0ee 100644
--- a/include/net/if_inet6.h
+++ b/include/net/if_inet6.h
@@ -89,10 +89,11 @@ struct ip6_sf_socklist {
 struct ipv6_mc_socklist {
         struct in6_addr         addr;
         int                     ifindex;
-        struct ipv6_mc_socklist *next;
+        struct ipv6_mc_socklist __rcu *next;
         rwlock_t                sflock;
         unsigned int            sfmode;         /* MCAST_{INCLUDE,EXCLUDE} */
         struct ip6_sf_socklist  *sflist;
+        struct rcu_head         rcu;
 };
 
 struct ip6_sf_list {
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 9c5074528a71..49f986d626a0 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -82,7 +82,7 @@ static void *__mld2_query_bugs[] __attribute__((__unused__)) = {
 static struct in6_addr mld2_all_mcr = MLD2_ALL_MCR_INIT;
 
 /* Big mc list lock for all the sockets */
-static DEFINE_RWLOCK(ipv6_sk_mc_lock);
+static DEFINE_SPINLOCK(ipv6_sk_mc_lock);
 
 static void igmp6_join_group(struct ifmcaddr6 *ma);
 static void igmp6_leave_group(struct ifmcaddr6 *ma);
@@ -123,6 +123,11 @@ int sysctl_mld_max_msf __read_mostly = IPV6_MLD_MAX_MSF;
  *      socket join on multicast group
  */
 
+#define for_each_pmc_rcu(np, pmc)                               \
+        for (pmc = rcu_dereference(np->ipv6_mc_list);           \
+             pmc != NULL;                                       \
+             pmc = rcu_dereference(pmc->next))
+
 int ipv6_sock_mc_join(struct sock *sk, int ifindex, const struct in6_addr *addr)
 {
         struct net_device *dev = NULL;
@@ -134,15 +139,15 @@ int ipv6_sock_mc_join(struct sock *sk, int ifindex, const struct in6_addr *addr)
         if (!ipv6_addr_is_multicast(addr))
                 return -EINVAL;
 
-        read_lock_bh(&ipv6_sk_mc_lock);
-        for (mc_lst=np->ipv6_mc_list; mc_lst; mc_lst=mc_lst->next) {
+        rcu_read_lock();
+        for_each_pmc_rcu(np, mc_lst) {
                 if ((ifindex == 0 || mc_lst->ifindex == ifindex) &&
                     ipv6_addr_equal(&mc_lst->addr, addr)) {
-                        read_unlock_bh(&ipv6_sk_mc_lock);
+                        rcu_read_unlock();
                         return -EADDRINUSE;
                 }
         }
-        read_unlock_bh(&ipv6_sk_mc_lock);
+        rcu_read_unlock();
 
         mc_lst = sock_kmalloc(sk, sizeof(struct ipv6_mc_socklist), GFP_KERNEL);
 
@@ -186,33 +191,41 @@ int ipv6_sock_mc_join(struct sock *sk, int ifindex, const struct in6_addr *addr)
                 return err;
         }
 
-        write_lock_bh(&ipv6_sk_mc_lock);
+        spin_lock(&ipv6_sk_mc_lock);
         mc_lst->next = np->ipv6_mc_list;
-        np->ipv6_mc_list = mc_lst;
-        write_unlock_bh(&ipv6_sk_mc_lock);
+        rcu_assign_pointer(np->ipv6_mc_list, mc_lst);
+        spin_unlock(&ipv6_sk_mc_lock);
 
         rcu_read_unlock();
 
         return 0;
 }
 
+static void ipv6_mc_socklist_reclaim(struct rcu_head *head)
+{
+        kfree(container_of(head, struct ipv6_mc_socklist, rcu));
+}
 /*
  *      socket leave on multicast group
  */
 int ipv6_sock_mc_drop(struct sock *sk, int ifindex, const struct in6_addr *addr)
 {
         struct ipv6_pinfo *np = inet6_sk(sk);
-        struct ipv6_mc_socklist *mc_lst, **lnk;
+        struct ipv6_mc_socklist *mc_lst;
+        struct ipv6_mc_socklist __rcu **lnk;
         struct net *net = sock_net(sk);
 
-        write_lock_bh(&ipv6_sk_mc_lock);
-        for (lnk = &np->ipv6_mc_list; (mc_lst = *lnk) !=NULL ; lnk = &mc_lst->next) {
+        spin_lock(&ipv6_sk_mc_lock);
+        for (lnk = &np->ipv6_mc_list;
+             (mc_lst = rcu_dereference_protected(*lnk,
+                        lockdep_is_held(&ipv6_sk_mc_lock))) !=NULL ;
+              lnk = &mc_lst->next) {
                 if ((ifindex == 0 || mc_lst->ifindex == ifindex) &&
                     ipv6_addr_equal(&mc_lst->addr, addr)) {
                         struct net_device *dev;
 
                         *lnk = mc_lst->next;
-                        write_unlock_bh(&ipv6_sk_mc_lock);
+                        spin_unlock(&ipv6_sk_mc_lock);
 
                         rcu_read_lock();
                         dev = dev_get_by_index_rcu(net, mc_lst->ifindex);
@@ -225,11 +238,12 @@ int ipv6_sock_mc_drop(struct sock *sk, int ifindex, const struct in6_addr *addr)
                         } else
                                 (void) ip6_mc_leave_src(sk, mc_lst, NULL);
                         rcu_read_unlock();
-                        sock_kfree_s(sk, mc_lst, sizeof(*mc_lst));
+                        atomic_sub(sizeof(*mc_lst), &sk->sk_omem_alloc);
+                        call_rcu(&mc_lst->rcu, ipv6_mc_socklist_reclaim);
                         return 0;
                 }
         }
-        write_unlock_bh(&ipv6_sk_mc_lock);
+        spin_unlock(&ipv6_sk_mc_lock);
 
         return -EADDRNOTAVAIL;
 }
@@ -272,12 +286,13 @@ void ipv6_sock_mc_close(struct sock *sk)
         struct ipv6_mc_socklist *mc_lst;
         struct net *net = sock_net(sk);
 
-        write_lock_bh(&ipv6_sk_mc_lock);
-        while ((mc_lst = np->ipv6_mc_list) != NULL) {
+        spin_lock(&ipv6_sk_mc_lock);
+        while ((mc_lst = rcu_dereference_protected(np->ipv6_mc_list,
+                                lockdep_is_held(&ipv6_sk_mc_lock))) != NULL) {
                 struct net_device *dev;
 
                 np->ipv6_mc_list = mc_lst->next;
-                write_unlock_bh(&ipv6_sk_mc_lock);
+                spin_unlock(&ipv6_sk_mc_lock);
 
                 rcu_read_lock();
                 dev = dev_get_by_index_rcu(net, mc_lst->ifindex);
@@ -290,11 +305,13 @@ void ipv6_sock_mc_close(struct sock *sk)
                 } else
                         (void) ip6_mc_leave_src(sk, mc_lst, NULL);
                 rcu_read_unlock();
-                sock_kfree_s(sk, mc_lst, sizeof(*mc_lst));
 
-                write_lock_bh(&ipv6_sk_mc_lock);
+                atomic_sub(sizeof(*mc_lst), &sk->sk_omem_alloc);
+                call_rcu(&mc_lst->rcu, ipv6_mc_socklist_reclaim);
+
+                spin_lock(&ipv6_sk_mc_lock);
         }
-        write_unlock_bh(&ipv6_sk_mc_lock);
+        spin_unlock(&ipv6_sk_mc_lock);
 }
 
 int ip6_mc_source(int add, int omode, struct sock *sk,
@@ -328,8 +345,7 @@ int ip6_mc_source(int add, int omode, struct sock *sk,
 
         err = -EADDRNOTAVAIL;
 
-        read_lock(&ipv6_sk_mc_lock);
-        for (pmc=inet6->ipv6_mc_list; pmc; pmc=pmc->next) {
+        for_each_pmc_rcu(inet6, pmc) {
                 if (pgsr->gsr_interface && pmc->ifindex != pgsr->gsr_interface)
                         continue;
                 if (ipv6_addr_equal(&pmc->addr, group))
@@ -428,7 +444,6 @@ int ip6_mc_source(int add, int omode, struct sock *sk,
 done:
         if (pmclocked)
                 write_unlock(&pmc->sflock);
-        read_unlock(&ipv6_sk_mc_lock);
         read_unlock_bh(&idev->lock);
         rcu_read_unlock();
         if (leavegroup)
@@ -466,14 +481,13 @@ int ip6_mc_msfilter(struct sock *sk, struct group_filter *gsf)
         dev = idev->dev;
 
         err = 0;
-        read_lock(&ipv6_sk_mc_lock);
 
         if (gsf->gf_fmode == MCAST_INCLUDE && gsf->gf_numsrc == 0) {
                 leavegroup = 1;
                 goto done;
         }
 
-        for (pmc=inet6->ipv6_mc_list; pmc; pmc=pmc->next) {
+        for_each_pmc_rcu(inet6, pmc) {
                 if (pmc->ifindex != gsf->gf_interface)
                         continue;
                 if (ipv6_addr_equal(&pmc->addr, group))
@@ -521,7 +535,6 @@ int ip6_mc_msfilter(struct sock *sk, struct group_filter *gsf)
         write_unlock(&pmc->sflock);
         err = 0;
 done:
-        read_unlock(&ipv6_sk_mc_lock);
         read_unlock_bh(&idev->lock);
         rcu_read_unlock();
         if (leavegroup)
@@ -562,7 +575,7 @@ int ip6_mc_msfget(struct sock *sk, struct group_filter *gsf,
          * so reading the list is safe.
          */
 
-        for (pmc=inet6->ipv6_mc_list; pmc; pmc=pmc->next) {
+        for_each_pmc_rcu(inet6, pmc) {
                 if (pmc->ifindex != gsf->gf_interface)
                         continue;
                 if (ipv6_addr_equal(group, &pmc->addr))
@@ -612,13 +625,13 @@ int inet6_mc_check(struct sock *sk, const struct in6_addr *mc_addr,
         struct ip6_sf_socklist *psl;
         int rv = 1;
 
-        read_lock(&ipv6_sk_mc_lock);
-        for (mc = np->ipv6_mc_list; mc; mc = mc->next) {
+        rcu_read_lock();
+        for_each_pmc_rcu(np, mc) {
                 if (ipv6_addr_equal(&mc->addr, mc_addr))
                         break;
         }
         if (!mc) {
-                read_unlock(&ipv6_sk_mc_lock);
+                rcu_read_unlock();
                 return 1;
         }
         read_lock(&mc->sflock);
@@ -638,7 +651,7 @@ int inet6_mc_check(struct sock *sk, const struct in6_addr *mc_addr,
                         rv = 0;
         }
         read_unlock(&mc->sflock);
-        read_unlock(&ipv6_sk_mc_lock);
+        rcu_read_unlock();
 
         return rv;
 }