ceph: handle partial result from get_user_pages

The get_user_pages() helper can return fewer than the requested pages.
Error out in that case, and clean up the partial result.
Signed-off-by: Henry C Chang <henry_c_chang@tcloudcomputing.com>
Signed-off-by: Sage Weil <sage@newdream.net>

net/ceph/pagevec.c

@@ -26,12 +26,12 @@ struct page **ceph_get_direct_page_vector(const char __user *data,
 	rc = get_user_pages(current, current->mm, (unsigned long)data,
 			    num_pages, write_page, 0, pages, NULL);
 	up_read(&current->mm->mmap_sem);
-	if (rc < 0)
+	if (rc < num_pages)
 		goto fail;
 	return pages;
 
 fail:
-	kfree(pages);
+	ceph_put_page_vector(pages, rc > 0 ? rc : 0, false);
 	return ERR_PTR(rc);
 }
 EXPORT_SYMBOL(ceph_get_direct_page_vector);