bonding: fix lock ordering for rtnl and bonding_rwsem

Fix the handling of rtnl and the bonding_rwsem to always be acquired
in a consistent order (rtnl, then bonding_rwsem).

The existing code sometimes acquired them in this order, and sometimes
in the opposite order, which opens a window for deadlock between ifenslave
and sysfs.

Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

1 files changed, 19 insertions, 0 deletions

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 379c5d87c804..2c6da4969382 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -4874,9 +4874,22 @@ static struct lock_class_key bonding_netdev_xmit_lock_key;
 int bond_create(char *name, struct bond_params *params, struct bonding **newbond)
 {
         struct net_device *bond_dev;
+        struct bonding *bond, *nxt;
         int res;
 
         rtnl_lock();
+        down_write(&bonding_rwsem);
+
+        /* Check to see if the bond already exists. */
+        list_for_each_entry_safe(bond, nxt, &bond_dev_list, bond_list)
+                if (strnicmp(bond->dev->name, name, IFNAMSIZ) == 0) {
+                        printk(KERN_ERR DRV_NAME
+                               ": cannot add bond %s; it already exists\n",
+                               name);
+                        res = -EPERM;
+                        goto out_rtnl;
+                }
+
         bond_dev = alloc_netdev(sizeof(struct bonding), name ? name : "",
                                 ether_setup);
         if (!bond_dev) {
@@ -4915,10 +4928,12 @@ int bond_create(char *name, struct bond_params *params, struct bonding **newbond
 
         netif_carrier_off(bond_dev);
 
+        up_write(&bonding_rwsem);
         rtnl_unlock(); /* allows sysfs registration of net device */
         res = bond_create_sysfs_entry(bond_dev->priv);
         if (res < 0) {
                 rtnl_lock();
+                down_write(&bonding_rwsem);
                 goto out_bond;
         }
 
@@ -4929,6 +4944,7 @@ out_bond:
 out_netdev:
         free_netdev(bond_dev);
 out_rtnl:
+        up_write(&bonding_rwsem);
         rtnl_unlock();
         return res;
 }
@@ -4949,6 +4965,9 @@ static int __init bonding_init(void)
 #ifdef CONFIG_PROC_FS
         bond_create_proc_dir();
 #endif
+
+        init_rwsem(&bonding_rwsem);
+
         for (i = 0; i < max_bonds; i++) {
                 res = bond_create(NULL, &bonding_defaults, NULL);
                 if (res)