[FIB]: Fix rcu_dereference() abuses in fib_trie.c

node_parent() and tnode_get_child() currently use rcu_dereference().

These functions are called from both
- readers only paths (where rcu_dereference() is needed), and
- writer path (where rcu_dereference() is not needed)

To make explicit where rcu_dereference() is really needed, I
introduced new node_parent_rcu() and tnode_get_child_rcu() functions
which use rcu_dereference(), while node_parent() and tnode_get_child()
dont use it.

Then I changed calling sites where rcu_dereference() was really needed
to call the _rcu() variants.

This should have no impact but for alpha architecture, and may help
future sparse checks.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index fbc80d15827b53319b69b3ef1432f3e50f44e5ca..a52334d30cf8ac6fc615cbe844c6b9bb3dc1bcae 100644 (file)
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -165,9 +165,13 @@ static struct kmem_cache *fn_alias_kmem __read_mostly;
 
 static inline struct tnode *node_parent(struct node *node)
 {
-       struct tnode *ret;
+       return (struct tnode *)(node->parent & ~NODE_TYPE_MASK);
+}
+
+static inline struct tnode *node_parent_rcu(struct node *node)
+{
+       struct tnode *ret = node_parent(node);
 
-       ret = (struct tnode *)(node->parent & ~NODE_TYPE_MASK);
        return rcu_dereference(ret);
 }
 
@@ -177,13 +181,18 @@ static inline void node_set_parent(struct node *node, struct tnode *ptr)
                           (unsigned long)ptr | NODE_TYPE(node));
 }
 
-/* rcu_read_lock needs to be hold by caller from readside */
+static inline struct node *tnode_get_child(struct tnode *tn, unsigned int i)
+{
+       BUG_ON(i >= 1U << tn->bits);
 
-static inline struct node *tnode_get_child(struct tnode *tn, int i)
+       return tn->child[i];
+}
+
+static inline struct node *tnode_get_child_rcu(struct tnode *tn, unsigned int i)
 {
-       BUG_ON(i >= 1 << tn->bits);
+       struct node *ret = tnode_get_child(tn, i);
 
-       return rcu_dereference(tn->child[i]);
+       return rcu_dereference(ret);
 }
 
 static inline int tnode_child_length(const struct tnode *tn)
@@ -938,7 +947,7 @@ fib_find_node(struct trie *t, u32 key)
 
                if (tkey_sub_equals(tn->key, pos, tn->pos-pos, key)) {
                        pos = tn->pos + tn->bits;
-                       n = tnode_get_child(tn, tkey_extract_bits(key, tn->pos, tn->bits));
+                       n = tnode_get_child_rcu(tn, tkey_extract_bits(key, tn->pos, tn->bits));
                } else
                        break;
        }
@@ -1688,7 +1697,7 @@ static struct leaf *nextleaf(struct trie *t, struct leaf *thisleaf)
 
                p = (struct tnode*) trie;  /* Start */
        } else
-               p = node_parent(c);
+               p = node_parent_rcu(c);
 
        while (p) {
                int pos, last;
@@ -1725,7 +1734,7 @@ static struct leaf *nextleaf(struct trie *t, struct leaf *thisleaf)
 up:
                /* No more children go up one step  */
                c = (struct node *) p;
-               p = node_parent(c);
+               p = node_parent_rcu(c);
        }
        return NULL; /* Ready. Root of trie */
 }
@@ -1987,7 +1996,7 @@ static struct node *fib_trie_get_next(struct fib_trie_iter *iter)
                 iter->tnode, iter->index, iter->depth);
 rescan:
        while (cindex < (1<<tn->bits)) {
-               struct node *n = tnode_get_child(tn, cindex);
+               struct node *n = tnode_get_child_rcu(tn, cindex);
 
                if (n) {
                        if (IS_LEAF(n)) {
@@ -2006,7 +2015,7 @@ rescan:
        }
 
        /* Current node exhausted, pop back up */
-       p = node_parent((struct node *)tn);
+       p = node_parent_rcu((struct node *)tn);
        if (p) {
                cindex = tkey_extract_bits(tn->key, p->pos, p->bits)+1;
                tn = p;
@@ -2315,7 +2324,7 @@ static int fib_trie_seq_show(struct seq_file *seq, void *v)
        if (v == SEQ_START_TOKEN)
                return 0;
 
-       if (!node_parent(n)) {
+       if (!node_parent_rcu(n)) {
                if (iter->trie == iter->trie_local)
                        seq_puts(seq, "<local>:\n");
                else