From: Herbert Xu Date: Fri, 14 Oct 2005 23:42:39 +0000 (+1000) Subject: [IPV4]: Kill redundant rcu_dereference on fa_info X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=1371e37da299d4df6267ad0ddf010435782c28e9;p=openwrt%2Fstaging%2Fblogic.git [IPV4]: Kill redundant rcu_dereference on fa_info This patch kills a redundant rcu_dereference on fa->fa_info in fib_trie.c. As this dereference directly follows a list_for_each_entry_rcu line, we have already taken a read barrier with respect to getting an entry from the list. This read barrier guarantees that all values read out of fa are valid. In particular, the contents of structure pointed to by fa->fa_info is initialised before fa->fa_info is actually set (see fn_trie_insert); the setting of fa->fa_info itself is further separated with a write barrier from the insertion of fa into the list. Therefore by taking a read barrier after obtaining fa from the list (which is given by list_for_each_entry_rcu), we can be sure that fa->fa_info contains a valid pointer, as well as the fact that the data pointed to by fa->fa_info is itself valid. Signed-off-by: Herbert Xu Acked-by: Paul E. McKenney Signed-off-by: David S. Miller Signed-off-by: Arnaldo Carvalho de Melo --- diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c index 0093ea08c7f5..66247f38b371 100644 --- a/net/ipv4/fib_trie.c +++ b/net/ipv4/fib_trie.c @@ -2404,7 +2404,7 @@ static int fib_route_seq_show(struct seq_file *seq, void *v) prefix = htonl(l->key); list_for_each_entry_rcu(fa, &li->falh, fa_list) { - const struct fib_info *fi = rcu_dereference(fa->fa_info); + const struct fib_info *fi = fa->fa_info; unsigned flags = fib_flag_trans(fa->fa_type, mask, fi); if (fa->fa_type == RTN_BROADCAST