Revert "fs: prevent speculative execution"

CVE-2017-5753 (revert embargoed)
CVE-2017-5715 (revert embargoed)

This reverts commit 905b2bac.
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

include/linux/fdtable.h

@@ -81,10 +81,8 @@ static inline struct file *__fcheck_files(struct files_struct *files, unsigned i
 {
 	struct fdtable *fdt = rcu_dereference_raw(files->fdt);
 
-	if (fd < fdt->max_fds) {
-		gmb();
+	if (fd < fdt->max_fds)
 		return rcu_dereference_raw(fdt->fd[fd]);
-	}
 	return NULL;
 }