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Message-ID: <1269206752.3004.9.camel@edumazet-laptop> Date: Sun, 21 Mar 2010 22:25:52 +0100 From: Eric Dumazet <eric.dumazet@...il.com> To: Andi Kleen <andi@...stfloor.org> Cc: robert.olsson@....uu.se, netdev@...r.kernel.org, paulmck@...ux.vnet.ibm.com Subject: Re: RCU problems in fib_table_insert Le dimanche 21 mars 2010 à 21:25 +0100, Andi Kleen a écrit : > Hi, > > I got the following warning at boot with a 2.6.34-rc2ish git kernel > with RCU debugging and preemption enabled. > > It seems the problem is that not all callers of fib_find_node > call it with rcu_read_lock() to stabilize access to the fib. > > I tried to fix it, but especially for fib_table_insert() that's rather > tricky: it does a lot of memory allocations and also route flushing and > other blocking operations while assuming the original fa is RCU stable. > > I first tried to move some allocations to the beginning and keep > preemption disabled in the rest, but it's difficult with all of them. > No patch because of that. > > Does the fa need an additional reference count for this problem? > Or perhaps some optimistic locking? > > -Andi No real changes needed, only a lockdep warning... Probably a rcu_dereference() should be changed to rcu_dereference_check() like we did for __in6_dev_get() We hold RTNL or rcu_read_lock [PATCH] net: fib_find_node() rcu check We hold rcu read lock or RTNL when fib_find_node() is called. Shutup lockdep complain. Reported-by: Andi Kleen <andi@...stfloor.org> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com> --- diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c index af5d897..471fe07 100644 --- a/net/ipv4/fib_trie.c +++ b/net/ipv4/fib_trie.c @@ -961,7 +961,8 @@ fib_find_node(struct trie *t, u32 key) struct node *n; pos = 0; - n = rcu_dereference(t->trie); + n = rcu_dereference_check(t->trie, + rcu_read_lock_held() || lockdep_rtnl_is_held()); while (n != NULL && NODE_TYPE(n) == T_TNODE) { tn = (struct tnode *) n; -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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