David Miller a écrit :
From: Eric Dumazet <[EMAIL PROTECTED]>
Date: Tue, 08 Jan 2008 07:11:30 +0100
@@ -288,15 +288,15 @@ static struct rtable *rt_cache_get_first(struct seq_file
*seq)
static struct rtable *rt_cache_get_next(struct seq_file *seq, struct rtable *r)
{
- struct rt_cache_iter_state *st = rcu_dereference(seq->private);
+ struct rt_cache_iter_state *st = seq->private;
Can you explain to me why this rcu_dereference() can be removed?
Very good question, but honestly I really dont see why it was there at the
first place :
"struct seq_file" is private to this thread, so seq.private is
also private and cannot change while this thread runs rt_cache_get_next().
Reading it once (as guaranted bu rcu_dereference()) or several time if
compiler really is dumb enough wont change the result...
The rest of your patch is OK and once I understand the above
I'll add it to net-2.6, thanks!
Maybe we can first have an Ack from Dipankar Sarma, I can repost the patch
with a more precise ChangeLog and wait his answer ?
[NET] ROUTE: fix rcu_dereference() uses in /proc/net/rt_cache
In rt_cache_get_next(), no need to guard seq->private by a rcu_dereference()
since seq is private to the thread running this function. Reading seq.private
once (as guaranted bu rcu_dereference()) or several time if compiler really is
dumb enough wont change the result.
But we miss real spots where rcu_dereference() are needed, both in
rt_cache_get_first() and rt_cache_get_next()
Signed-off-by: Eric Dumazet <[EMAIL PROTECTED]>
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index d337706..3b7562f 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -278,7 +278,7 @@ static struct rtable *rt_cache_get_first(struct seq_file
*seq)
for (st->bucket = rt_hash_mask; st->bucket >= 0; --st->bucket) {
rcu_read_lock_bh();
- r = rt_hash_table[st->bucket].chain;
+ r = rcu_dereference(rt_hash_table[st->bucket].chain);
if (r)
break;
rcu_read_unlock_bh();
@@ -288,15 +288,15 @@ static struct rtable *rt_cache_get_first(struct seq_file
*seq)
static struct rtable *rt_cache_get_next(struct seq_file *seq, struct rtable *r)
{
- struct rt_cache_iter_state *st = rcu_dereference(seq->private);
+ struct rt_cache_iter_state *st = seq->private;
- r = r->u.dst.rt_next;
+ r = rcu_dereference(r->u.dst.rt_next);
while (!r) {
rcu_read_unlock_bh();
if (--st->bucket < 0)
break;
rcu_read_lock_bh();
- r = rt_hash_table[st->bucket].chain;
+ r = rcu_dereference(rt_hash_table[st->bucket].chain);
}
return r;
}
