bridge: use _bh spinlock variant for br_fdb_update to avoid lockup

commit 1d7c49037b12016e7056b9f2c990380e2187e766 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 use spin_lock_bh 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. These locks 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")

Signed-off-by: Wilson Kok <wkok@cumulusnetworks.com>
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Fixes: 292d1398983f ("bridge: add NTF_USE support")
Signed-off-by: David S. Miller <davem@davemloft.net>
[lizf: Backported to 3.4: adjust context]
Signed-off-by: Zefan Li <lizefan@huawei.com>

diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
index 5ba0c844d508cbe549788e2219b4dd9ab1383149..b5597bb37e7a2962c646df104f173fc15f7a4607 100644 (file)
--- a/net/bridge/br_fdb.c
+++ b/net/bridge/br_fdb.c
@@ -440,7 +440,7 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
                        fdb->updated = jiffies;
                }
        } else {
-               spin_lock(&br->hash_lock);
+               spin_lock_bh(&br->hash_lock);
                if (likely(!fdb_find(head, addr))) {
                        fdb = fdb_create(head, source, addr);
                        if (fdb)
@@ -449,7 +449,7 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
                /* else  we lose race and someone else inserts
                 * it first, don't bother updating
                 */
-               spin_unlock(&br->hash_lock);
+               spin_unlock_bh(&br->hash_lock);
        }
 }