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Date: Mon, 23 Jun 2008 12:36:50 +1000
From: Nick Piggin <nickpiggin@...oo.com.au>
To: Lai Jiangshan <laijs@...fujitsu.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Luis Carlos Cobo <luisca@...ybit.com>,
Steve Whitehouse <SteveW@....org>,
Alexey Kuznetsov <kuznet@....inr.ac.ru>,
Nick Piggin <npiggin@...e.de>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH]rcu,inet,fib_trie,route,radix-tree,DECnet,mac80211: fix meaningless rcu_dereference(local_var)
On Saturday 21 June 2008 19:54, Lai Jiangshan wrote:
> diff --git a/lib/radix-tree.c b/lib/radix-tree.c
> index 169a2f8..bfae4e2 100644
> --- a/lib/radix-tree.c
> +++ b/lib/radix-tree.c
> @@ -703,9 +703,9 @@ __lookup(struct radix_tree_node *slot, void **results,
> unsigned long index, for (i = index & RADIX_TREE_MAP_MASK; i <
> RADIX_TREE_MAP_SIZE; i++) { struct radix_tree_node *node;
> index++;
> - node = slot->slots[i];
> + node = rcu_dereference(slot->slots[i]);
> if (node) {
> - results[nr_found++] = rcu_dereference(node);
> + results[nr_found++] = node;
> if (nr_found == max_items)
> goto out;
> }
> @@ -815,7 +815,7 @@ __lookup_tag(struct radix_tree_node *slot, void
> **results, unsigned long index, index++;
> if (!tag_get(slot, tag, j))
> continue;
> - node = slot->slots[j];
> + node = rcu_dereference(slot->slots[j]);
> /*
> * Even though the tag was found set, we need to
> * recheck that we have a non-NULL node, because
> @@ -827,7 +827,6 @@ __lookup_tag(struct radix_tree_node *slot, void
> **results, unsigned long index, * rely on its value remaining the same).
> */
> if (node) {
> - node = rcu_dereference(node);
> results[nr_found++] = node;
> if (nr_found == max_items)
> goto out;
This was done like this IIRC to avoid the barrier when possible.
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