Re: [PATCH net v2 2/2] lwtunnel: Fix oops on state free after encap module unload

[Robert Shearman]

On 23/01/17 20:42, David Miller wrote:

From: Robert Shearman <rshea...@brocade.com>
Date: Sat, 21 Jan 2017 00:21:26 +0000

@@ -115,8 +115,12 @@ int lwtunnel_build_state(struct net_device *dev, u16 
encap_type,
        ret = -EOPNOTSUPP;
        rcu_read_lock();

Here 'ret' equals -EOPNOTSUPP

        ops = rcu_dereference(lwtun_encaps[encap_type]);
-       if (likely(ops && ops->build_state))
-               ret = ops->build_state(dev, encap, family, cfg, lws);
+       if (likely(ops)) {
+               if (likely(try_module_get(ops->owner) && ops->build_state))
+                       ret = ops->build_state(dev, encap, family, cfg, lws);
+               if (ret)
+                       module_put(ops->owner);

If try_module_get() fails, 'ret' will still be -EOPNOTSUPP and we will
module_put() on a module we did not grab a reference to.

I think you need to adjust the logic here.  You only want to 'put' if
try_module_get() succeeds and ->build_state() returns an error.

Indeed, good point. Will address in a v3 shortly.

Thanks,
Rob