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Commit b59cfbf7 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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[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: default avatarEric Dumazet <dada1@cosmosbay.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 95b7d924

net/ipv4/fib_trie.c

+21 −12
Original line number Diff line number Diff line
@@ -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 @@ static struct node *fib_trie_get_next(struct fib_trie_iter *iter) 
	}



	/* 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