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>

1 files changed, 33 insertions, 11 deletions

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 57f09ea3ef2a..bf490d0c98c6 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -158,6 +158,32 @@ xprt_class_release(const struct xprt_class *t)
 }
 
 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)
 {
 	const struct xprt_class *t;
@@ -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)