SUNRPC: Close a race with transport setup and module put

After we've looked up the transport module, we need to ensure it can't
go away until we've finished running the transport setup code.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 57f09ea3ef2af761e726579c6e7a1a70693f9b48..bf490d0c98c6a62a2da2e59a9c812c9c85fff23b 100644 (file)
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -157,6 +157,32 @@ xprt_class_release(const struct xprt_class *t)
        module_put(t->owner);
 }
 
+static const struct xprt_class *
+xprt_class_find_by_ident_locked(int ident)
+{
+       const struct xprt_class *t;
+
+       list_for_each_entry(t, &xprt_list, list) {
+               if (t->ident != ident)
+                       continue;
+               if (!try_module_get(t->owner))
+                       continue;
+               return t;
+       }
+       return NULL;
+}
+
+static const struct xprt_class *
+xprt_class_find_by_ident(int ident)
+{
+       const struct xprt_class *t;
+
+       spin_lock(&xprt_list_lock);
+       t = xprt_class_find_by_ident_locked(ident);
+       spin_unlock(&xprt_list_lock);
+       return t;
+}
+
 static const struct xprt_class *
 xprt_class_find_by_netid_locked(const char *netid)
 {
@@ -1929,21 +1955,17 @@ static void xprt_init(struct rpc_xprt *xprt, struct net *net)
 struct rpc_xprt *xprt_create_transport(struct xprt_create *args)
 {
        struct rpc_xprt *xprt;
-       struct xprt_class *t;
+       const struct xprt_class *t;
 
-       spin_lock(&xprt_list_lock);
-       list_for_each_entry(t, &xprt_list, list) {
-               if (t->ident == args->ident) {
-                       spin_unlock(&xprt_list_lock);
-                       goto found;
-               }
+       t = xprt_class_find_by_ident(args->ident);
+       if (!t) {
+               dprintk("RPC: transport (%d) not supported\n", args->ident);
+               return ERR_PTR(-EIO);
        }
-       spin_unlock(&xprt_list_lock);
-       dprintk("RPC: transport (%d) not supported\n", args->ident);
-       return ERR_PTR(-EIO);
 
-found:
        xprt = t->setup(args);
+       xprt_class_release(t);
+
        if (IS_ERR(xprt))
                goto out;
        if (args->flags & XPRT_CREATE_NO_IDLE_TIMEOUT)