afs: Fix afs_server_list to be cleaned up with RCU

afs_server_list is accessed with the rcu_read_lock() held from
volume->servers, so it needs to be cleaned up correctly.

Fix this by using kfree_rcu() instead of kfree().

Fixes: 8a070a96 ("afs: Detect cell aliases 1 - Cells with root volumes")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org

fs/afs/internal.h

@@ -553,6 +553,7 @@ struct afs_server_entry {
 };
 
 struct afs_server_list {
+	struct rcu_head		rcu;
 	afs_volid_t		vids[AFS_MAXTYPES]; /* Volume IDs */
 	refcount_t		usage;
 	unsigned char		nr_servers;

fs/afs/server_list.c

@@ -17,7 +17,7 @@ void afs_put_serverlist(struct afs_net *net, struct afs_server_list *slist)
 		for (i = 0; i < slist->nr_servers; i++)
 			afs_unuse_server(net, slist->servers[i].server,
 					 afs_server_trace_put_slist);
-		kfree(slist);
+		kfree_rcu(slist, rcu);
 	}
 }