fib_hash: RCU conversion phase 1

First step for RCU conversion of fib_hash :

struct fn_zone are created and never deleted.

Very classic conversion, using rcu_assign_pointer(), rcu_dereference()
and rtnl_dereference() verbs.

__rcu markers on fz_next and fn_zone_list

They are created under RTNL, we dont need fib_hash_lock anymore in
fn_new_zone().

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

1 files changed, 38 insertions, 19 deletions

diff --git a/net/ipv4/fib_hash.c b/net/ipv4/fib_hash.c
index 10001aa40692..04f05a96b75b 100644
--- a/net/ipv4/fib_hash.c
+++ b/net/ipv4/fib_hash.c
@@ -57,7 +57,7 @@ struct fib_node {
 #define EMBEDDED_HASH_SIZE (L1_CACHE_BYTES / sizeof(struct hlist_head))
 
 struct fn_zone {
-        struct fn_zone          *fz_next;       /* Next not empty zone  */
+        struct fn_zone __rcu    *fz_next;       /* Next not empty zone  */
         struct hlist_head       *fz_hash;       /* Hash table pointer   */
         u32                     fz_hashmask;    /* (fz_divisor - 1)     */
 
@@ -73,8 +73,8 @@ struct fn_zone {
 };
 
 struct fn_hash {
-        struct fn_zone  *fn_zones[33];
-        struct fn_zone  *fn_zone_list;
+        struct fn_zone          *fn_zones[33];
+        struct fn_zone __rcu    *fn_zone_list;
 };
 
 static inline u32 fn_hash(__be32 key, struct fn_zone *fz)
@@ -219,21 +219,21 @@ fn_new_zone(struct fn_hash *table, int z)
         fz->fz_mask = inet_make_mask(z);
 
         /* Find the first not empty zone with more specific mask */
-        for (i=z+1; i<=32; i++)
+        for (i = z + 1; i <= 32; i++)
                 if (table->fn_zones[i])
                         break;
-        write_lock_bh(&fib_hash_lock);
-        if (i>32) {
+        if (i > 32) {
                 /* No more specific masks, we are the first. */
-                fz->fz_next = table->fn_zone_list;
-                table->fn_zone_list = fz;
+                rcu_assign_pointer(fz->fz_next,
+                                   rtnl_dereference(table->fn_zone_list));
+                rcu_assign_pointer(table->fn_zone_list, fz);
         } else {
-                fz->fz_next = table->fn_zones[i]->fz_next;
-                table->fn_zones[i]->fz_next = fz;
+                rcu_assign_pointer(fz->fz_next,
+                                   rtnl_dereference(table->fn_zones[i]->fz_next));
+                rcu_assign_pointer(table->fn_zones[i]->fz_next, fz);
         }
         table->fn_zones[z] = fz;
         fib_hash_genid++;
-        write_unlock_bh(&fib_hash_lock);
         return fz;
 }
 
@@ -245,8 +245,11 @@ int fib_table_lookup(struct fib_table *tb,
         struct fn_zone *fz;
         struct fn_hash *t = (struct fn_hash *)tb->tb_data;
 
+        rcu_read_lock();
         read_lock(&fib_hash_lock);
-        for (fz = t->fn_zone_list; fz; fz = fz->fz_next) {
+        for (fz = rcu_dereference(t->fn_zone_list);
+             fz != NULL;
+             fz = rcu_dereference(fz->fz_next)) {
                 struct hlist_head *head;
                 struct hlist_node *node;
                 struct fib_node *f;
@@ -267,6 +270,7 @@ int fib_table_lookup(struct fib_table *tb,
         err = 1;
 out:
         read_unlock(&fib_hash_lock);
+        rcu_read_unlock();
         return err;
 }
 
@@ -362,6 +366,7 @@ static struct fib_node *fib_find_node(struct fn_zone *fz, __be32 key)
         return NULL;
 }
 
+/* Caller must hold RTNL. */
 int fib_table_insert(struct fib_table *tb, struct fib_config *cfg)
 {
         struct fn_hash *table = (struct fn_hash *) tb->tb_data;
@@ -657,13 +662,16 @@ static int fn_flush_list(struct fn_zone *fz, int idx)
         return found;
 }
 
+/* caller must hold RTNL. */
 int fib_table_flush(struct fib_table *tb)
 {
         struct fn_hash *table = (struct fn_hash *) tb->tb_data;
         struct fn_zone *fz;
         int found = 0;
 
-        for (fz = table->fn_zone_list; fz; fz = fz->fz_next) {
+        for (fz = rtnl_dereference(table->fn_zone_list);
+             fz != NULL;
+             fz = rtnl_dereference(fz->fz_next)) {
                 int i;
 
                 for (i = fz->fz_divisor - 1; i >= 0; i--)
@@ -741,23 +749,29 @@ fn_hash_dump_zone(struct sk_buff *skb, struct netlink_callback *cb,
 int fib_table_dump(struct fib_table *tb, struct sk_buff *skb,
                    struct netlink_callback *cb)
 {
-        int m, s_m;
+        int m = 0, s_m;
         struct fn_zone *fz;
         struct fn_hash *table = (struct fn_hash *)tb->tb_data;
 
         s_m = cb->args[2];
+        rcu_read_lock();
         read_lock(&fib_hash_lock);
-        for (fz = table->fn_zone_list, m=0; fz; fz = fz->fz_next, m++) {
-                if (m < s_m) continue;
+        for (fz = rcu_dereference(table->fn_zone_list);
+             fz != NULL;
+             fz = rcu_dereference(fz->fz_next), m++) {
+                if (m < s_m)
+                        continue;
                 if (fn_hash_dump_zone(skb, cb, tb, fz) < 0) {
                         cb->args[2] = m;
                         read_unlock(&fib_hash_lock);
+                        rcu_read_unlock();
                         return -1;
                 }
                 memset(&cb->args[3], 0,
                        sizeof(cb->args) - 3*sizeof(cb->args[0]));
         }
         read_unlock(&fib_hash_lock);
+        rcu_read_unlock();
         cb->args[2] = m;
         return skb->len;
 }
@@ -820,8 +834,9 @@ static struct fib_alias *fib_get_first(struct seq_file *seq)
         iter->genid     = fib_hash_genid;
         iter->valid     = 1;
 
-        for (iter->zone = table->fn_zone_list; iter->zone;
-             iter->zone = iter->zone->fz_next) {
+        for (iter->zone = rcu_dereference(table->fn_zone_list);
+             iter->zone != NULL;
+             iter->zone = rcu_dereference(iter->zone->fz_next)) {
                 int maxslot;
 
                 if (!iter->zone->fz_nent)
@@ -906,7 +921,7 @@ static struct fib_alias *fib_get_next(struct seq_file *seq)
                         }
                 }
 
-                iter->zone = iter->zone->fz_next;
+                iter->zone = rcu_dereference(iter->zone->fz_next);
 
                 if (!iter->zone)
                         goto out;
@@ -946,9 +961,11 @@ static struct fib_alias *fib_get_idx(struct seq_file *seq, loff_t pos)
 
 static void *fib_seq_start(struct seq_file *seq, loff_t *pos)
         __acquires(fib_hash_lock)
+        __acquires(RCU)
 {
         void *v = NULL;
 
+        rcu_read_lock();
         read_lock(&fib_hash_lock);
         if (fib_get_table(seq_file_net(seq), RT_TABLE_MAIN))
                 v = *pos ? fib_get_idx(seq, *pos - 1) : SEQ_START_TOKEN;
@@ -963,8 +980,10 @@ static void *fib_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 
 static void fib_seq_stop(struct seq_file *seq, void *v)
         __releases(fib_hash_lock)
+        __releases(RCU)
 {
         read_unlock(&fib_hash_lock);
+        rcu_read_unlock();
 }
 
 static unsigned fib_flag_trans(int type, __be32 mask, struct fib_info *fi)