[NETFILTER]: nf_conntrack: fix smp_processor_id() in preemptible code warning

Since we're using RCU for the conntrack hash now, we need to avoid
getting preempted or interrupted by BHs while changing the stats.

Fixes warning reported by Tilman Schmidt <tilman@imap.cc> when using
preemptible RCU:

[   48.180297] BUG: using smp_processor_id() in preemptible [00000000] code: ntpdate/3562
[   48.180297] caller is __nf_conntrack_find+0x9b/0xeb [nf_conntrack]
[   48.180297] Pid: 3562, comm: ntpdate Not tainted 2.6.25-rc2-mm1-testing #1
[   48.180297]  [<c02015b9>] debug_smp_processor_id+0x99/0xb0
[   48.180297]  [<fac643a7>] __nf_conntrack_find+0x9b/0xeb [nf_conntrack]
Tested-by: NTilman Schmidt <tilman@imap.cc>
Tested-by: Christian Casteyde <casteyde.christian@free.fr> [Bugzilla #10097]
Signed-off-by: NPatrick McHardy <kaber@trash.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/netfilter/nf_conntrack_core.c

@@ -256,13 +256,19 @@ __nf_conntrack_find(const struct nf_conntrack_tuple *tuple)
 	struct hlist_node *n;
 	unsigned int hash = hash_conntrack(tuple);
 
+	/* Disable BHs the entire time since we normally need to disable them
+	 * at least once for the stats anyway.
+	 */
+	local_bh_disable();
 	hlist_for_each_entry_rcu(h, n, &nf_conntrack_hash[hash], hnode) {
 		if (nf_ct_tuple_equal(tuple, &h->tuple)) {
 			NF_CT_STAT_INC(found);
+			local_bh_enable();
 			return h;
 		}
 		NF_CT_STAT_INC(searched);
 	}
+	local_bh_enable();
 
 	return NULL;
 }
@@ -400,17 +406,20 @@ nf_conntrack_tuple_taken(const struct nf_conntrack_tuple *tuple,
 	struct hlist_node *n;
 	unsigned int hash = hash_conntrack(tuple);
 
-	rcu_read_lock();
+	/* Disable BHs the entire time since we need to disable them at
+	 * least once for the stats anyway.
+	 */
+	rcu_read_lock_bh();
 	hlist_for_each_entry_rcu(h, n, &nf_conntrack_hash[hash], hnode) {
 		if (nf_ct_tuplehash_to_ctrack(h) != ignored_conntrack &&
 		    nf_ct_tuple_equal(tuple, &h->tuple)) {
 			NF_CT_STAT_INC(found);
-			rcu_read_unlock();
+			rcu_read_unlock_bh();
 			return 1;
 		}
 		NF_CT_STAT_INC(searched);
 	}
-	rcu_read_unlock();
+	rcu_read_unlock_bh();
 
 	return 0;
 }