igmp: RCU conversion of in_dev->mc_list

in_dev->mc_list is protected by one rwlock (in_dev->mc_list_lock).

This can easily be converted to a RCU protection.

Writers hold RTNL, so mc_list_lock is removed, not replaced by a
spinlock.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Cypher Wu <cypher.w@gmail.com>
Cc: Américo Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 104 insertions, 119 deletions

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 08d0d81ffc15..6f49d6c087da 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -149,11 +149,17 @@ static void ip_mc_clear_src(struct ip_mc_list *pmc);
 static int ip_mc_add_src(struct in_device *in_dev, __be32 *pmca, int sfmode,
                          int sfcount, __be32 *psfsrc, int delta);
 
+
+static void ip_mc_list_reclaim(struct rcu_head *head)
+{
+        kfree(container_of(head, struct ip_mc_list, rcu));
+}
+
 static void ip_ma_put(struct ip_mc_list *im)
 {
         if (atomic_dec_and_test(&im->refcnt)) {
                 in_dev_put(im->interface);
-                kfree(im);
+                call_rcu(&im->rcu, ip_mc_list_reclaim);
         }
 }
 
@@ -163,7 +169,7 @@ static void ip_ma_put(struct ip_mc_list *im)
  *      Timer management
  */
 
-static __inline__ void igmp_stop_timer(struct ip_mc_list *im)
+static void igmp_stop_timer(struct ip_mc_list *im)
 {
         spin_lock_bh(&im->lock);
         if (del_timer(&im->timer))
@@ -496,14 +502,24 @@ empty_source:
         return skb;
 }
 
+#define for_each_pmc_rcu(in_dev, pmc)                           \
+        for (pmc = rcu_dereference(in_dev->mc_list);            \
+             pmc != NULL;                                       \
+             pmc = rcu_dereference(pmc->next_rcu))
+
+#define for_each_pmc_rtnl(in_dev, pmc)                          \
+        for (pmc = rtnl_dereference(in_dev->mc_list);           \
+             pmc != NULL;                                       \
+             pmc = rtnl_dereference(pmc->next_rcu))
+
 static int igmpv3_send_report(struct in_device *in_dev, struct ip_mc_list *pmc)
 {
         struct sk_buff *skb = NULL;
         int type;
 
         if (!pmc) {
-                read_lock(&in_dev->mc_list_lock);
-                for (pmc=in_dev->mc_list; pmc; pmc=pmc->next) {
+                rcu_read_lock();
+                for_each_pmc_rcu(in_dev, pmc) {
                         if (pmc->multiaddr == IGMP_ALL_HOSTS)
                                 continue;
                         spin_lock_bh(&pmc->lock);
@@ -514,7 +530,7 @@ static int igmpv3_send_report(struct in_device *in_dev, struct ip_mc_list *pmc)
                         skb = add_grec(skb, pmc, type, 0, 0);
                         spin_unlock_bh(&pmc->lock);
                 }
-                read_unlock(&in_dev->mc_list_lock);
+                rcu_read_unlock();
         } else {
                 spin_lock_bh(&pmc->lock);
                 if (pmc->sfcount[MCAST_EXCLUDE])
@@ -556,7 +572,7 @@ static void igmpv3_send_cr(struct in_device *in_dev)
         struct sk_buff *skb = NULL;
         int type, dtype;
 
-        read_lock(&in_dev->mc_list_lock);
+        rcu_read_lock();
         spin_lock_bh(&in_dev->mc_tomb_lock);
 
         /* deleted MCA's */
@@ -593,7 +609,7 @@ static void igmpv3_send_cr(struct in_device *in_dev)
         spin_unlock_bh(&in_dev->mc_tomb_lock);
 
         /* change recs */
-        for (pmc=in_dev->mc_list; pmc; pmc=pmc->next) {
+        for_each_pmc_rcu(in_dev, pmc) {
                 spin_lock_bh(&pmc->lock);
                 if (pmc->sfcount[MCAST_EXCLUDE]) {
                         type = IGMPV3_BLOCK_OLD_SOURCES;
@@ -616,7 +632,7 @@ static void igmpv3_send_cr(struct in_device *in_dev)
                 }
                 spin_unlock_bh(&pmc->lock);
         }
-        read_unlock(&in_dev->mc_list_lock);
+        rcu_read_unlock();
 
         if (!skb)
                 return;
@@ -813,14 +829,14 @@ static void igmp_heard_report(struct in_device *in_dev, __be32 group)
         if (group == IGMP_ALL_HOSTS)
                 return;
 
-        read_lock(&in_dev->mc_list_lock);
-        for (im=in_dev->mc_list; im!=NULL; im=im->next) {
+        rcu_read_lock();
+        for_each_pmc_rcu(in_dev, im) {
                 if (im->multiaddr == group) {
                         igmp_stop_timer(im);
                         break;
                 }
         }
-        read_unlock(&in_dev->mc_list_lock);
+        rcu_read_unlock();
 }
 
 static void igmp_heard_query(struct in_device *in_dev, struct sk_buff *skb,
@@ -906,8 +922,8 @@ static void igmp_heard_query(struct in_device *in_dev, struct sk_buff *skb,
          * - Use the igmp->igmp_code field as the maximum
          *   delay possible
          */
-        read_lock(&in_dev->mc_list_lock);
-        for (im=in_dev->mc_list; im!=NULL; im=im->next) {
+        rcu_read_lock();
+        for_each_pmc_rcu(in_dev, im) {
                 int changed;
 
                 if (group && group != im->multiaddr)
@@ -925,7 +941,7 @@ static void igmp_heard_query(struct in_device *in_dev, struct sk_buff *skb,
                 if (changed)
                         igmp_mod_timer(im, max_delay);
         }
-        read_unlock(&in_dev->mc_list_lock);
+        rcu_read_unlock();
 }
 
 /* called in rcu_read_lock() section */
@@ -1110,8 +1126,8 @@ static void igmpv3_clear_delrec(struct in_device *in_dev)
                 kfree(pmc);
         }
         /* clear dead sources, too */
-        read_lock(&in_dev->mc_list_lock);
-        for (pmc=in_dev->mc_list; pmc; pmc=pmc->next) {
+        rcu_read_lock();
+        for_each_pmc_rcu(in_dev, pmc) {
                 struct ip_sf_list *psf, *psf_next;
 
                 spin_lock_bh(&pmc->lock);
@@ -1123,7 +1139,7 @@ static void igmpv3_clear_delrec(struct in_device *in_dev)
                         kfree(psf);
                 }
         }
-        read_unlock(&in_dev->mc_list_lock);
+        rcu_read_unlock();
 }
 #endif
 
@@ -1209,7 +1225,7 @@ void ip_mc_inc_group(struct in_device *in_dev, __be32 addr)
 
         ASSERT_RTNL();
 
-        for (im=in_dev->mc_list; im; im=im->next) {
+        for_each_pmc_rtnl(in_dev, im) {
                 if (im->multiaddr == addr) {
                         im->users++;
                         ip_mc_add_src(in_dev, &addr, MCAST_EXCLUDE, 0, NULL, 0);
@@ -1217,7 +1233,7 @@ void ip_mc_inc_group(struct in_device *in_dev, __be32 addr)
                 }
         }
 
-        im = kmalloc(sizeof(*im), GFP_KERNEL);
+        im = kzalloc(sizeof(*im), GFP_KERNEL);
         if (!im)
                 goto out;
 
@@ -1227,26 +1243,18 @@ void ip_mc_inc_group(struct in_device *in_dev, __be32 addr)
         im->multiaddr = addr;
         /* initial mode is (EX, empty) */
         im->sfmode = MCAST_EXCLUDE;
-        im->sfcount[MCAST_INCLUDE] = 0;
         im->sfcount[MCAST_EXCLUDE] = 1;
-        im->sources = NULL;
-        im->tomb = NULL;
-        im->crcount = 0;
         atomic_set(&im->refcnt, 1);
         spin_lock_init(&im->lock);
 #ifdef CONFIG_IP_MULTICAST
-        im->tm_running = 0;
         setup_timer(&im->timer, &igmp_timer_expire, (unsigned long)im);
         im->unsolicit_count = IGMP_Unsolicited_Report_Count;
-        im->reporter = 0;
-        im->gsquery = 0;
 #endif
-        im->loaded = 0;
-        write_lock_bh(&in_dev->mc_list_lock);
-        im->next = in_dev->mc_list;
-        in_dev->mc_list = im;
+
+        im->next_rcu = in_dev->mc_list;
         in_dev->mc_count++;
-        write_unlock_bh(&in_dev->mc_list_lock);
+        rcu_assign_pointer(in_dev->mc_list, im);
+
 #ifdef CONFIG_IP_MULTICAST
         igmpv3_del_delrec(in_dev, im->multiaddr);
 #endif
@@ -1287,17 +1295,18 @@ EXPORT_SYMBOL(ip_mc_rejoin_group);
 
 void ip_mc_dec_group(struct in_device *in_dev, __be32 addr)
 {
-        struct ip_mc_list *i, **ip;
+        struct ip_mc_list *i;
+        struct ip_mc_list __rcu **ip;
 
         ASSERT_RTNL();
 
-        for (ip=&in_dev->mc_list; (i=*ip)!=NULL; ip=&i->next) {
+        for (ip = &in_dev->mc_list;
+             (i = rtnl_dereference(*ip)) != NULL;
+             ip = &i->next_rcu) {
                 if (i->multiaddr == addr) {
                         if (--i->users == 0) {
-                                write_lock_bh(&in_dev->mc_list_lock);
-                                *ip = i->next;
+                                *ip = i->next_rcu;
                                 in_dev->mc_count--;
-                                write_unlock_bh(&in_dev->mc_list_lock);
                                 igmp_group_dropped(i);
 
                                 if (!in_dev->dead)
@@ -1316,34 +1325,34 @@ EXPORT_SYMBOL(ip_mc_dec_group);
 
 void ip_mc_unmap(struct in_device *in_dev)
 {
-        struct ip_mc_list *i;
+        struct ip_mc_list *pmc;
 
         ASSERT_RTNL();
 
-        for (i = in_dev->mc_list; i; i = i->next)
-                igmp_group_dropped(i);
+        for_each_pmc_rtnl(in_dev, pmc)
+                igmp_group_dropped(pmc);
 }
 
 void ip_mc_remap(struct in_device *in_dev)
 {
-        struct ip_mc_list *i;
+        struct ip_mc_list *pmc;
 
         ASSERT_RTNL();
 
-        for (i = in_dev->mc_list; i; i = i->next)
-                igmp_group_added(i);
+        for_each_pmc_rtnl(in_dev, pmc)
+                igmp_group_added(pmc);
 }
 
 /* Device going down */
 
 void ip_mc_down(struct in_device *in_dev)
 {
-        struct ip_mc_list *i;
+        struct ip_mc_list *pmc;
 
         ASSERT_RTNL();
 
-        for (i=in_dev->mc_list; i; i=i->next)
-                igmp_group_dropped(i);
+        for_each_pmc_rtnl(in_dev, pmc)
+                igmp_group_dropped(pmc);
 
 #ifdef CONFIG_IP_MULTICAST
         in_dev->mr_ifc_count = 0;
@@ -1374,7 +1383,6 @@ void ip_mc_init_dev(struct in_device *in_dev)
         in_dev->mr_qrv = IGMP_Unsolicited_Report_Count;
 #endif
 
-        rwlock_init(&in_dev->mc_list_lock);
         spin_lock_init(&in_dev->mc_tomb_lock);
 }
 
@@ -1382,14 +1390,14 @@ void ip_mc_init_dev(struct in_device *in_dev)
 
 void ip_mc_up(struct in_device *in_dev)
 {
-        struct ip_mc_list *i;
+        struct ip_mc_list *pmc;
 
         ASSERT_RTNL();
 
         ip_mc_inc_group(in_dev, IGMP_ALL_HOSTS);
 
-        for (i=in_dev->mc_list; i; i=i->next)
-                igmp_group_added(i);
+        for_each_pmc_rtnl(in_dev, pmc)
+                igmp_group_added(pmc);
 }
 
 /*
@@ -1405,17 +1413,13 @@ void ip_mc_destroy_dev(struct in_device *in_dev)
         /* Deactivate timers */
         ip_mc_down(in_dev);
 
-        write_lock_bh(&in_dev->mc_list_lock);
-        while ((i = in_dev->mc_list) != NULL) {
-                in_dev->mc_list = i->next;
+        while ((i = rtnl_dereference(in_dev->mc_list)) != NULL) {
+                in_dev->mc_list = i->next_rcu;
                 in_dev->mc_count--;
-                write_unlock_bh(&in_dev->mc_list_lock);
+
                 igmp_group_dropped(i);
                 ip_ma_put(i);
-
-                write_lock_bh(&in_dev->mc_list_lock);
         }
-        write_unlock_bh(&in_dev->mc_list_lock);
 }
 
 /* RTNL is locked */
@@ -1513,18 +1517,18 @@ static int ip_mc_del_src(struct in_device *in_dev, __be32 *pmca, int sfmode,
 
         if (!in_dev)
                 return -ENODEV;
-        read_lock(&in_dev->mc_list_lock);
-        for (pmc=in_dev->mc_list; pmc; pmc=pmc->next) {
+        rcu_read_lock();
+        for_each_pmc_rcu(in_dev, pmc) {
                 if (*pmca == pmc->multiaddr)
                         break;
         }
         if (!pmc) {
                 /* MCA not found?? bug */
-                read_unlock(&in_dev->mc_list_lock);
+                rcu_read_unlock();
                 return -ESRCH;
         }
         spin_lock_bh(&pmc->lock);
-        read_unlock(&in_dev->mc_list_lock);
+        rcu_read_unlock();
 #ifdef CONFIG_IP_MULTICAST
         sf_markstate(pmc);
 #endif
@@ -1685,18 +1689,18 @@ static int ip_mc_add_src(struct in_device *in_dev, __be32 *pmca, int sfmode,
 
         if (!in_dev)
                 return -ENODEV;
-        read_lock(&in_dev->mc_list_lock);
-        for (pmc=in_dev->mc_list; pmc; pmc=pmc->next) {
+        rcu_read_lock();
+        for_each_pmc_rcu(in_dev, pmc) {
                 if (*pmca == pmc->multiaddr)
                         break;
         }
         if (!pmc) {
                 /* MCA not found?? bug */
-                read_unlock(&in_dev->mc_list_lock);
+                rcu_read_unlock();
                 return -ESRCH;
         }
         spin_lock_bh(&pmc->lock);
-        read_unlock(&in_dev->mc_list_lock);
+        rcu_read_unlock();
 
 #ifdef CONFIG_IP_MULTICAST
         sf_markstate(pmc);
@@ -1793,7 +1797,7 @@ int ip_mc_join_group(struct sock *sk , struct ip_mreqn *imr)
 
         err = -EADDRINUSE;
         ifindex = imr->imr_ifindex;
-        for (i = inet->mc_list; i; i = i->next) {
+        for_each_pmc_rtnl(inet, i) {
                 if (i->multi.imr_multiaddr.s_addr == addr &&
                     i->multi.imr_ifindex == ifindex)
                         goto done;
@@ -1807,7 +1811,7 @@ int ip_mc_join_group(struct sock *sk , struct ip_mreqn *imr)
                 goto done;
 
         memcpy(&iml->multi, imr, sizeof(*imr));
-        iml->next = inet->mc_list;
+        iml->next_rcu = inet->mc_list;
         iml->sflist = NULL;
         iml->sfmode = MCAST_EXCLUDE;
         rcu_assign_pointer(inet->mc_list, iml);
@@ -1821,17 +1825,14 @@ EXPORT_SYMBOL(ip_mc_join_group);
 
 static void ip_sf_socklist_reclaim(struct rcu_head *rp)
 {
-        struct ip_sf_socklist *psf;
-
-        psf = container_of(rp, struct ip_sf_socklist, rcu);
+        kfree(container_of(rp, struct ip_sf_socklist, rcu));
         /* sk_omem_alloc should have been decreased by the caller*/
-        kfree(psf);
 }
 
 static int ip_mc_leave_src(struct sock *sk, struct ip_mc_socklist *iml,
                            struct in_device *in_dev)
 {
-        struct ip_sf_socklist *psf = iml->sflist;
+        struct ip_sf_socklist *psf = rtnl_dereference(iml->sflist);
         int err;
 
         if (psf == NULL) {
@@ -1851,11 +1852,8 @@ static int ip_mc_leave_src(struct sock *sk, struct ip_mc_socklist *iml,
 
 static void ip_mc_socklist_reclaim(struct rcu_head *rp)
 {
-        struct ip_mc_socklist *iml;
-
-        iml = container_of(rp, struct ip_mc_socklist, rcu);
+        kfree(container_of(rp, struct ip_mc_socklist, rcu));
         /* sk_omem_alloc should have been decreased by the caller*/
-        kfree(iml);
 }
 
 
@@ -1866,7 +1864,8 @@ static void ip_mc_socklist_reclaim(struct rcu_head *rp)
 int ip_mc_leave_group(struct sock *sk, struct ip_mreqn *imr)
 {
         struct inet_sock *inet = inet_sk(sk);
-        struct ip_mc_socklist *iml, **imlp;
+        struct ip_mc_socklist *iml;
+        struct ip_mc_socklist __rcu **imlp;
         struct in_device *in_dev;
         struct net *net = sock_net(sk);
         __be32 group = imr->imr_multiaddr.s_addr;
@@ -1876,7 +1875,9 @@ int ip_mc_leave_group(struct sock *sk, struct ip_mreqn *imr)
         rtnl_lock();
         in_dev = ip_mc_find_dev(net, imr);
         ifindex = imr->imr_ifindex;
-        for (imlp = &inet->mc_list; (iml = *imlp) != NULL; imlp = &iml->next) {
+        for (imlp = &inet->mc_list;
+             (iml = rtnl_dereference(*imlp)) != NULL;
+             imlp = &iml->next_rcu) {
                 if (iml->multi.imr_multiaddr.s_addr != group)
                         continue;
                 if (ifindex) {
@@ -1888,7 +1889,7 @@ int ip_mc_leave_group(struct sock *sk, struct ip_mreqn *imr)
 
                 (void) ip_mc_leave_src(sk, iml, in_dev);
 
-                rcu_assign_pointer(*imlp, iml->next);
+                *imlp = iml->next_rcu;
 
                 if (in_dev)
                         ip_mc_dec_group(in_dev, group);
@@ -1934,7 +1935,7 @@ int ip_mc_source(int add, int omode, struct sock *sk, struct
         }
         err = -EADDRNOTAVAIL;
 
-        for (pmc=inet->mc_list; pmc; pmc=pmc->next) {
+        for_each_pmc_rtnl(inet, pmc) {
                 if ((pmc->multi.imr_multiaddr.s_addr ==
                      imr.imr_multiaddr.s_addr) &&
                     (pmc->multi.imr_ifindex == imr.imr_ifindex))
@@ -1958,7 +1959,7 @@ int ip_mc_source(int add, int omode, struct sock *sk, struct
                 pmc->sfmode = omode;
         }
 
-        psl = pmc->sflist;
+        psl = rtnl_dereference(pmc->sflist);
         if (!add) {
                 if (!psl)
                         goto done;      /* err = -EADDRNOTAVAIL */
@@ -2077,7 +2078,7 @@ int ip_mc_msfilter(struct sock *sk, struct ip_msfilter *msf, int ifindex)
                 goto done;
         }
 
-        for (pmc=inet->mc_list; pmc; pmc=pmc->next) {
+        for_each_pmc_rtnl(inet, pmc) {
                 if (pmc->multi.imr_multiaddr.s_addr == msf->imsf_multiaddr &&
                     pmc->multi.imr_ifindex == imr.imr_ifindex)
                         break;
@@ -2107,7 +2108,7 @@ int ip_mc_msfilter(struct sock *sk, struct ip_msfilter *msf, int ifindex)
                 (void) ip_mc_add_src(in_dev, &msf->imsf_multiaddr,
                                      msf->imsf_fmode, 0, NULL, 0);
         }
-        psl = pmc->sflist;
+        psl = rtnl_dereference(pmc->sflist);
         if (psl) {
                 (void) ip_mc_del_src(in_dev, &msf->imsf_multiaddr, pmc->sfmode,
                         psl->sl_count, psl->sl_addr, 0);
@@ -2155,7 +2156,7 @@ int ip_mc_msfget(struct sock *sk, struct ip_msfilter *msf,
         }
         err = -EADDRNOTAVAIL;
 
-        for (pmc=inet->mc_list; pmc; pmc=pmc->next) {
+        for_each_pmc_rtnl(inet, pmc) {
                 if (pmc->multi.imr_multiaddr.s_addr == msf->imsf_multiaddr &&
                     pmc->multi.imr_ifindex == imr.imr_ifindex)
                         break;
@@ -2163,7 +2164,7 @@ int ip_mc_msfget(struct sock *sk, struct ip_msfilter *msf,
         if (!pmc)               /* must have a prior join */
                 goto done;
         msf->imsf_fmode = pmc->sfmode;
-        psl = pmc->sflist;
+        psl = rtnl_dereference(pmc->sflist);
         rtnl_unlock();
         if (!psl) {
                 len = 0;
@@ -2208,7 +2209,7 @@ int ip_mc_gsfget(struct sock *sk, struct group_filter *gsf,
 
         err = -EADDRNOTAVAIL;
 
-        for (pmc=inet->mc_list; pmc; pmc=pmc->next) {
+        for_each_pmc_rtnl(inet, pmc) {
                 if (pmc->multi.imr_multiaddr.s_addr == addr &&
                     pmc->multi.imr_ifindex == gsf->gf_interface)
                         break;
@@ -2216,7 +2217,7 @@ int ip_mc_gsfget(struct sock *sk, struct group_filter *gsf,
         if (!pmc)               /* must have a prior join */
                 goto done;
         gsf->gf_fmode = pmc->sfmode;
-        psl = pmc->sflist;
+        psl = rtnl_dereference(pmc->sflist);
         rtnl_unlock();
         count = psl ? psl->sl_count : 0;
         copycount = count < gsf->gf_numsrc ? count : gsf->gf_numsrc;
@@ -2257,7 +2258,7 @@ int ip_mc_sf_allow(struct sock *sk, __be32 loc_addr, __be32 rmt_addr, int dif)
                 goto out;
 
         rcu_read_lock();
-        for (pmc=rcu_dereference(inet->mc_list); pmc; pmc=rcu_dereference(pmc->next)) {
+        for_each_pmc_rcu(inet, pmc) {
                 if (pmc->multi.imr_multiaddr.s_addr == loc_addr &&
                     pmc->multi.imr_ifindex == dif)
                         break;
@@ -2265,7 +2266,7 @@ int ip_mc_sf_allow(struct sock *sk, __be32 loc_addr, __be32 rmt_addr, int dif)
         ret = inet->mc_all;
         if (!pmc)
                 goto unlock;
-        psl = pmc->sflist;
+        psl = rcu_dereference(pmc->sflist);
         ret = (pmc->sfmode == MCAST_EXCLUDE);
         if (!psl)
                 goto unlock;
@@ -2300,10 +2301,10 @@ void ip_mc_drop_socket(struct sock *sk)
                 return;
 
         rtnl_lock();
-        while ((iml = inet->mc_list) != NULL) {
+        while ((iml = rtnl_dereference(inet->mc_list)) != NULL) {
                 struct in_device *in_dev;
-                rcu_assign_pointer(inet->mc_list, iml->next);
 
+                inet->mc_list = iml->next_rcu;
                 in_dev = inetdev_by_index(net, iml->multi.imr_ifindex);
                 (void) ip_mc_leave_src(sk, iml, in_dev);
                 if (in_dev != NULL) {
@@ -2323,8 +2324,8 @@ int ip_check_mc(struct in_device *in_dev, __be32 mc_addr, __be32 src_addr, u16 p
         struct ip_sf_list *psf;
         int rv = 0;
 
-        read_lock(&in_dev->mc_list_lock);
-        for (im=in_dev->mc_list; im; im=im->next) {
+        rcu_read_lock();
+        for_each_pmc_rcu(in_dev, im) {
                 if (im->multiaddr == mc_addr)
                         break;
         }
@@ -2345,7 +2346,7 @@ int ip_check_mc(struct in_device *in_dev, __be32 mc_addr, __be32 src_addr, u16 p
                 } else
                         rv = 1; /* unspecified source; tentatively allow */
         }
-        read_unlock(&in_dev->mc_list_lock);
+        rcu_read_unlock();
         return rv;
 }
 
@@ -2371,13 +2372,11 @@ static inline struct ip_mc_list *igmp_mc_get_first(struct seq_file *seq)
                 in_dev = __in_dev_get_rcu(state->dev);
                 if (!in_dev)
                         continue;
-                read_lock(&in_dev->mc_list_lock);
-                im = in_dev->mc_list;
+                im = rcu_dereference(in_dev->mc_list);
                 if (im) {
                         state->in_dev = in_dev;
                         break;
                 }
-                read_unlock(&in_dev->mc_list_lock);
         }
         return im;
 }
@@ -2385,11 +2384,9 @@ static inline struct ip_mc_list *igmp_mc_get_first(struct seq_file *seq)
 static struct ip_mc_list *igmp_mc_get_next(struct seq_file *seq, struct ip_mc_list *im)
 {
         struct igmp_mc_iter_state *state = igmp_mc_seq_private(seq);
-        im = im->next;
-        while (!im) {
-                if (likely(state->in_dev != NULL))
-                        read_unlock(&state->in_dev->mc_list_lock);
 
+        im = rcu_dereference(im->next_rcu);
+        while (!im) {
                 state->dev = next_net_device_rcu(state->dev);
                 if (!state->dev) {
                         state->in_dev = NULL;
@@ -2398,8 +2395,7 @@ static struct ip_mc_list *igmp_mc_get_next(struct seq_file *seq, struct ip_mc_li
                 state->in_dev = __in_dev_get_rcu(state->dev);
                 if (!state->in_dev)
                         continue;
-                read_lock(&state->in_dev->mc_list_lock);
-                im = state->in_dev->mc_list;
+                im = rcu_dereference(state->in_dev->mc_list);
         }
         return im;
 }
@@ -2435,10 +2431,8 @@ static void igmp_mc_seq_stop(struct seq_file *seq, void *v)
         __releases(rcu)
 {
         struct igmp_mc_iter_state *state = igmp_mc_seq_private(seq);
-        if (likely(state->in_dev != NULL)) {
-                read_unlock(&state->in_dev->mc_list_lock);
-                state->in_dev = NULL;
-        }
+
+        state->in_dev = NULL;
         state->dev = NULL;
         rcu_read_unlock();
 }
@@ -2460,7 +2454,7 @@ static int igmp_mc_seq_show(struct seq_file *seq, void *v)
                 querier = "NONE";
 #endif
 
-                if (state->in_dev->mc_list == im) {
+                if (rcu_dereference(state->in_dev->mc_list) == im) {
                         seq_printf(seq, "%d\t%-10s: %5d %7s\n",
                                    state->dev->ifindex, state->dev->name, state->in_dev->mc_count, querier);
                 }
@@ -2519,8 +2513,7 @@ static inline struct ip_sf_list *igmp_mcf_get_first(struct seq_file *seq)
                 idev = __in_dev_get_rcu(state->dev);
                 if (unlikely(idev == NULL))
                         continue;
-                read_lock(&idev->mc_list_lock);
-                im = idev->mc_list;
+                im = rcu_dereference(idev->mc_list);
                 if (likely(im != NULL)) {
                         spin_lock_bh(&im->lock);
                         psf = im->sources;
@@ -2531,7 +2524,6 @@ static inline struct ip_sf_list *igmp_mcf_get_first(struct seq_file *seq)
                         }
                         spin_unlock_bh(&im->lock);
                 }
-                read_unlock(&idev->mc_list_lock);
         }
         return psf;
 }
@@ -2545,9 +2537,6 @@ static struct ip_sf_list *igmp_mcf_get_next(struct seq_file *seq, struct ip_sf_l
                 spin_unlock_bh(&state->im->lock);
                 state->im = state->im->next;
                 while (!state->im) {
-                        if (likely(state->idev != NULL))
-                                read_unlock(&state->idev->mc_list_lock);
-
                         state->dev = next_net_device_rcu(state->dev);
                         if (!state->dev) {
                                 state->idev = NULL;
@@ -2556,8 +2545,7 @@ static struct ip_sf_list *igmp_mcf_get_next(struct seq_file *seq, struct ip_sf_l
                         state->idev = __in_dev_get_rcu(state->dev);
                         if (!state->idev)
                                 continue;
-                        read_lock(&state->idev->mc_list_lock);
-                        state->im = state->idev->mc_list;
+                        state->im = rcu_dereference(state->idev->mc_list);
                 }
                 if (!state->im)
                         break;
@@ -2603,10 +2591,7 @@ static void igmp_mcf_seq_stop(struct seq_file *seq, void *v)
                 spin_unlock_bh(&state->im->lock);
                 state->im = NULL;
         }
-        if (likely(state->idev != NULL)) {
-                read_unlock(&state->idev->mc_list_lock);
-                state->idev = NULL;
-        }
+        state->idev = NULL;
         state->dev = NULL;
         rcu_read_unlock();
 }