From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Curt Brune , Scott Feldman , "David S. Miller" Subject: [PATCH 3.4 20/27] bridge: use spin_lock_bh() in br_multicast_set_hash_max Date: Mon, 13 Jan 2014 16:26:34 -0800 Message-Id: <20140114002623.955760413@linuxfoundation.org> In-Reply-To: <20140114002623.356220317@linuxfoundation.org> References: <20140114002623.356220317@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Curt Brune [ Upstream commit fe0d692bbc645786bce1a98439e548ae619269f5 ] 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 Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/bridge/br_multicast.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/net/bridge/br_multicast.c +++ b/net/bridge/br_multicast.c @@ -1744,7 +1744,7 @@ int br_multicast_set_hash_max(struct net 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; @@ -1776,7 +1776,7 @@ rollback: } unlock: - spin_unlock(&br->multicast_lock); + spin_unlock_bh(&br->multicast_lock); return err; }