From mboxrd@z Thu Jan 1 00:00:00 1970 From: Scott Feldman Subject: [PATCH net-next 1/2] bridge: use spin_lock_bh() in br_multicast_set_hash_max Date: Mon, 06 Jan 2014 11:00:32 -0800 Message-ID: <20140106190032.10912.1521.stgit@monster-03.cumulusnetworks.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, roopa@cumulusnetworks.com, bridge@lists.linux-foundation.org, curt@cumulusnetworks.com, shm@cumulusnetworks.com To: stephen@networkplumber.org Return-path: Received: from ext3.cumulusnetworks.com ([198.211.106.187]:56987 "EHLO ext3.cumulusnetworks.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754221AbaAFTAn (ORCPT ); Mon, 6 Jan 2014 14:00:43 -0500 Sender: netdev-owner@vger.kernel.org List-ID: From: Curt Brune br_multicast_set_hash_max() is called from process context in net/bridge/br_sysfs_br.c by the sysfs store_hash_max() function. br_multicast_set_hash_max() calls spin_lock(&br->multicast_lock), which can deadlock the CPU if a softirq that also tries to take the same lock interrupts br_multicast_set_hash_max() while the lock is held . This can happen quite easily when any of the bridge multicast timers expire, which try to take the same lock. The fix here is to use spin_lock_bh(), preventing other softirqs from executing on this CPU. Steps to reproduce: 1. Create a bridge with several interfaces (I used 4). 2. Set the "multicast query interval" to a low number, like 2. 3. Enable the bridge as a multicast querier. 4. Repeatedly set the bridge hash_max parameter via sysfs. # brctl addbr br0 # brctl addif br0 eth1 eth2 eth3 eth4 # brctl setmcqi br0 2 # brctl setmcquerier br0 1 # while true ; do echo 4096 > /sys/class/net/br0/bridge/hash_max; done Signed-off-by: Curt Brune Signed-off-by: Scott Feldman --- net/bridge/br_multicast.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c index 4c214b2..ef66365 100644 --- a/net/bridge/br_multicast.c +++ b/net/bridge/br_multicast.c @@ -1998,7 +1998,7 @@ int br_multicast_set_hash_max(struct net_bridge *br, unsigned long val) u32 old; struct net_bridge_mdb_htable *mdb; - spin_lock(&br->multicast_lock); + spin_lock_bh(&br->multicast_lock); if (!netif_running(br->dev)) goto unlock; @@ -2030,7 +2030,7 @@ rollback: } unlock: - spin_unlock(&br->multicast_lock); + spin_unlock_bh(&br->multicast_lock); return err; }