decnet: RCU conversion and get rid of dev_base_lock

While tracking dev_base_lock users, I found decnet used it in
dnet_select_source(), but for a wrong purpose:

Writers only hold RTNL, not dev_base_lock, so readers must use RCU if
they cannot use RTNL.

Adds an rcu_head in struct dn_ifaddr and handle proper RCU management.

Adds __rcu annotation in dn_route as well.

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

1 files changed, 39 insertions, 29 deletions

diff --git a/net/decnet/dn_route.c b/net/decnet/dn_route.c
index df0f3e54ff8a..94a9eb1d313e 100644
--- a/net/decnet/dn_route.c
+++ b/net/decnet/dn_route.c
@@ -93,7 +93,7 @@
 
 struct dn_rt_hash_bucket
 {
-        struct dn_route *chain;
+        struct dn_route __rcu *chain;
         spinlock_t lock;
 };
 
@@ -157,15 +157,17 @@ static inline void dnrt_drop(struct dn_route *rt)
 static void dn_dst_check_expire(unsigned long dummy)
 {
         int i;
-        struct dn_route *rt, **rtp;
+        struct dn_route *rt;
+        struct dn_route __rcu **rtp;
         unsigned long now = jiffies;
         unsigned long expire = 120 * HZ;
 
-        for(i = 0; i <= dn_rt_hash_mask; i++) {
+        for (i = 0; i <= dn_rt_hash_mask; i++) {
                 rtp = &dn_rt_hash_table[i].chain;
 
                 spin_lock(&dn_rt_hash_table[i].lock);
-                while((rt=*rtp) != NULL) {
+                while ((rt = rcu_dereference_protected(*rtp,
+                                                lockdep_is_held(&dn_rt_hash_table[i].lock))) != NULL) {
                         if (atomic_read(&rt->dst.__refcnt) ||
                                         (now - rt->dst.lastuse) < expire) {
                                 rtp = &rt->dst.dn_next;
@@ -186,17 +188,19 @@ static void dn_dst_check_expire(unsigned long dummy)
 
 static int dn_dst_gc(struct dst_ops *ops)
 {
-        struct dn_route *rt, **rtp;
+        struct dn_route *rt;
+        struct dn_route __rcu **rtp;
         int i;
         unsigned long now = jiffies;
         unsigned long expire = 10 * HZ;
 
-        for(i = 0; i <= dn_rt_hash_mask; i++) {
+        for (i = 0; i <= dn_rt_hash_mask; i++) {
 
                 spin_lock_bh(&dn_rt_hash_table[i].lock);
                 rtp = &dn_rt_hash_table[i].chain;
 
-                while((rt=*rtp) != NULL) {
+                while ((rt = rcu_dereference_protected(*rtp,
+                                                lockdep_is_held(&dn_rt_hash_table[i].lock))) != NULL) {
                         if (atomic_read(&rt->dst.__refcnt) ||
                                         (now - rt->dst.lastuse) < expire) {
                                 rtp = &rt->dst.dn_next;
@@ -227,7 +231,7 @@ static void dn_dst_update_pmtu(struct dst_entry *dst, u32 mtu)
 {
         u32 min_mtu = 230;
         struct dn_dev *dn = dst->neighbour ?
-                            (struct dn_dev *)dst->neighbour->dev->dn_ptr : NULL;
+                            rcu_dereference_raw(dst->neighbour->dev->dn_ptr) : NULL;
 
         if (dn && dn->use_long == 0)
                 min_mtu -= 6;
@@ -277,13 +281,15 @@ static inline int compare_keys(struct flowi *fl1, struct flowi *fl2)
 
 static int dn_insert_route(struct dn_route *rt, unsigned hash, struct dn_route **rp)
 {
-        struct dn_route *rth, **rthp;
+        struct dn_route *rth;
+        struct dn_route __rcu **rthp;
         unsigned long now = jiffies;
 
         rthp = &dn_rt_hash_table[hash].chain;
 
         spin_lock_bh(&dn_rt_hash_table[hash].lock);
-        while((rth = *rthp) != NULL) {
+        while ((rth = rcu_dereference_protected(*rthp,
+                                                lockdep_is_held(&dn_rt_hash_table[hash].lock))) != NULL) {
                 if (compare_keys(&rth->fl, &rt->fl)) {
                         /* Put it first */
                         *rthp = rth->dst.dn_next;
@@ -315,15 +321,15 @@ static void dn_run_flush(unsigned long dummy)
         int i;
         struct dn_route *rt, *next;
 
-        for(i = 0; i < dn_rt_hash_mask; i++) {
+        for (i = 0; i < dn_rt_hash_mask; i++) {
                 spin_lock_bh(&dn_rt_hash_table[i].lock);
 
-                if ((rt = xchg(&dn_rt_hash_table[i].chain, NULL)) == NULL)
+                if ((rt = xchg((struct dn_route **)&dn_rt_hash_table[i].chain, NULL)) == NULL)
                         goto nothing_to_declare;
 
-                for(; rt; rt=next) {
-                        next = rt->dst.dn_next;
-                        rt->dst.dn_next = NULL;
+                for(; rt; rt = next) {
+                        next = rcu_dereference_raw(rt->dst.dn_next);
+                        RCU_INIT_POINTER(rt->dst.dn_next, NULL);
                         dst_free((struct dst_entry *)rt);
                 }
 
@@ -458,15 +464,16 @@ static int dn_return_long(struct sk_buff *skb)
  */
 static int dn_route_rx_packet(struct sk_buff *skb)
 {
-        struct dn_skb_cb *cb = DN_SKB_CB(skb);
+        struct dn_skb_cb *cb;
         int err;
 
         if ((err = dn_route_input(skb)) == 0)
                 return dst_input(skb);
 
+        cb = DN_SKB_CB(skb);
         if (decnet_debug_level & 4) {
                 char *devname = skb->dev ? skb->dev->name : "???";
-                struct dn_skb_cb *cb = DN_SKB_CB(skb);
+
                 printk(KERN_DEBUG
                         "DECnet: dn_route_rx_packet: rt_flags=0x%02x dev=%s len=%d src=0x%04hx dst=0x%04hx err=%d type=%d\n",
                         (int)cb->rt_flags, devname, skb->len,
@@ -573,7 +580,7 @@ int dn_route_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type
         struct dn_skb_cb *cb;
         unsigned char flags = 0;
         __u16 len = le16_to_cpu(*(__le16 *)skb->data);
-        struct dn_dev *dn = (struct dn_dev *)dev->dn_ptr;
+        struct dn_dev *dn = rcu_dereference(dev->dn_ptr);
         unsigned char padlen = 0;
 
         if (!net_eq(dev_net(dev), &init_net))
@@ -728,7 +735,7 @@ static int dn_forward(struct sk_buff *skb)
 {
         struct dn_skb_cb *cb = DN_SKB_CB(skb);
         struct dst_entry *dst = skb_dst(skb);
-        struct dn_dev *dn_db = dst->dev->dn_ptr;
+        struct dn_dev *dn_db = rcu_dereference(dst->dev->dn_ptr);
         struct dn_route *rt;
         struct neighbour *neigh = dst->neighbour;
         int header_len;
@@ -835,13 +842,16 @@ static inline int dn_match_addr(__le16 addr1, __le16 addr2)
 static __le16 dnet_select_source(const struct net_device *dev, __le16 daddr, int scope)
 {
         __le16 saddr = 0;
-        struct dn_dev *dn_db = dev->dn_ptr;
+        struct dn_dev *dn_db;
         struct dn_ifaddr *ifa;
         int best_match = 0;
         int ret;
 
-        read_lock(&dev_base_lock);
-        for(ifa = dn_db->ifa_list; ifa; ifa = ifa->ifa_next) {
+        rcu_read_lock();
+        dn_db = rcu_dereference(dev->dn_ptr);
+        for (ifa = rcu_dereference(dn_db->ifa_list);
+             ifa != NULL;
+             ifa = rcu_dereference(ifa->ifa_next)) {
                 if (ifa->ifa_scope > scope)
                         continue;
                 if (!daddr) {
@@ -854,7 +864,7 @@ static __le16 dnet_select_source(const struct net_device *dev, __le16 daddr, int
                 if (best_match == 0)
                         saddr = ifa->ifa_local;
         }
-        read_unlock(&dev_base_lock);
+        rcu_read_unlock();
 
         return saddr;
 }
@@ -1020,7 +1030,7 @@ source_ok:
                 err = -ENODEV;
                 if (dev_out == NULL)
                         goto out;
-                dn_db = dev_out->dn_ptr;
+                dn_db = rcu_dereference_raw(dev_out->dn_ptr);
                 /* Possible improvement - check all devices for local addr */
                 if (dn_dev_islocal(dev_out, fl.fld_dst)) {
                         dev_put(dev_out);
@@ -1233,7 +1243,7 @@ static int dn_route_input_slow(struct sk_buff *skb)
 
         dev_hold(in_dev);
 
-        if ((dn_db = in_dev->dn_ptr) == NULL)
+        if ((dn_db = rcu_dereference(in_dev->dn_ptr)) == NULL)
                 goto out;
 
         /* Zero source addresses are not allowed */
@@ -1677,15 +1687,15 @@ static struct dn_route *dn_rt_cache_get_next(struct seq_file *seq, struct dn_rou
 {
         struct dn_rt_cache_iter_state *s = seq->private;
 
-        rt = rt->dst.dn_next;
-        while(!rt) {
+        rt = rcu_dereference_bh(rt->dst.dn_next);
+        while (!rt) {
                 rcu_read_unlock_bh();
                 if (--s->bucket < 0)
                         break;
                 rcu_read_lock_bh();
-                rt = dn_rt_hash_table[s->bucket].chain;
+                rt = rcu_dereference_bh(dn_rt_hash_table[s->bucket].chain);
         }
-        return rcu_dereference_bh(rt);
+        return rt;
 }
 
 static void *dn_rt_cache_seq_start(struct seq_file *seq, loff_t *pos)