netfilter: nftables: comment indirect serialization of commit_mutex with rtnl_mutex

Add an explicit comment in the code to describe the indirect
serialization of the holders of the commit_mutex with the rtnl_mutex.
Commit 90d2723c6d4c ("netfilter: nf_tables: do not hold reference on
netdevice from preparation phase") already describes this, but a comment
in this case is better for reference.

Reported-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index c2f5987..9a08076 100644 (file)
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -1723,6 +1723,10 @@ static struct nft_hook *nft_netdev_hook_alloc(struct net *net,
        }
 
        nla_strlcpy(ifname, attr, IFNAMSIZ);
+       /* nf_tables_netdev_event() is called under rtnl_mutex, this is
+        * indirectly serializing all the other holders of the commit_mutex with
+        * the rtnl_mutex.
+        */
        dev = __dev_get_by_name(net, ifname);
        if (!dev) {
                err = -ENOENT;