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Date:	Thu, 21 May 2009 12:19:20 +0200
From:	Robert Olsson <>
Cc:	Robert Olsson <>,
	NetDEV list <>,
Subject: Re: [oops] with FIB_TRIE [PATCH]


Andrei Popa:
 > clear ip bgp * soft"
 > when I have three full BGP sessions the kernel it oopses. 

 It seems we can fix this by disabling preemption while we re-balance the 
 trie. This is with the CONFIG_CLASSIC_RCU. It's been stress-tested at high 
 loads continuesly taking a full BGP table up/down via iproute -batch.
 A patch is below.

 Note. fib_trie is not updated for CONFIG_PREEMPT_RCU

Signed-off-by: Robert Olsson <>

diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index ec0ae49..33c7c85 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -986,9 +986,12 @@ fib_find_node(struct trie *t, u32 key)
 static struct node *trie_rebalance(struct trie *t, struct tnode *tn)
 	int wasfull;
-	t_key cindex, key = tn->key;
+	t_key cindex, key;
 	struct tnode *tp;
+	preempt_disable();
+	key = tn->key;
 	while (tn != NULL && (tp = node_parent((struct node *)tn)) != NULL) {
 		cindex = tkey_extract_bits(key, tp->pos, tp->bits);
 		wasfull = tnode_full(tp, tnode_get_child(tp, cindex));
@@ -1007,6 +1010,7 @@ static struct node *trie_rebalance(struct trie *t, struct tnode *tn)
 	if (IS_TNODE(tn))
 		tn = (struct tnode *)resize(t, (struct tnode *)tn);
+	preempt_enable();
 	return (struct node *)tn;

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