From 4845c5376dbbf46853b53d5241fbe4d4a2c94b59 Mon Sep 17 00:00:00 2001 From: Nikolay Aleksandrov Date: Sat, 6 Jun 2015 06:49:00 -0700 Subject: [PATCH] bridge: disable softirqs around br_fdb_update to avoid lockup commit c4c832f89dc468cf11dc0dd17206bace44526651 upstream. br_fdb_update() can be called in process context in the following way: br_fdb_add() -> __br_fdb_add() -> br_fdb_update() (if NTF_USE flag is set) so we need to disable softirqs because there are softirq users of the hash_lock. One easy way to reproduce this is to modify the bridge utility to set NTF_USE, enable stp and then set maxageing to a low value so br_fdb_cleanup() is called frequently and then just add new entries in a loop. This happens because br_fdb_cleanup() is called from timer/softirq context. The spin locks in br_fdb_update were _bh before commit f8ae737deea1 ("[BRIDGE]: forwarding remove unneeded preempt and bh diasables") and at the time that commit was correct because br_fdb_update() couldn't be called from process context, but that changed after commit: 292d1398983f ("bridge: add NTF_USE support") Using local_bh_disable/enable around br_fdb_update() allows us to keep using the spin_lock/unlock in br_fdb_update for the fast-path. Signed-off-by: Nikolay Aleksandrov Fixes: 292d1398983f ("bridge: add NTF_USE support") Signed-off-by: David S. Miller [lizf: Backported to 3.4: adjust context] Signed-off-by: Zefan Li --- net/bridge/br_fdb.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c index b5597bb37e7a..3cb93e85d221 100644 --- a/net/bridge/br_fdb.c +++ b/net/bridge/br_fdb.c @@ -665,9 +665,11 @@ int br_fdb_add(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg) } if (ndm->ndm_flags & NTF_USE) { + local_bh_disable(); rcu_read_lock(); br_fdb_update(p->br, p, addr); rcu_read_unlock(); + local_bh_enable(); } else { spin_lock_bh(&p->br->hash_lock); err = fdb_add_entry(p, addr, ndm->ndm_state, nlh->nlmsg_flags);