NFS: Fix a memory leak in nfs_readdir

We need to ensure that the entries in the nfs_cache_array get cleared
when the page is removed from the page cache. To do so, we use the
freepage address_space operation.

Change nfs_readdir_clear_array to use kmap_atomic(), so that the
function can be safely called from all contexts.

Finally, modify the cache_page_release helper to call
nfs_readdir_clear_array directly, when dealing with an anonymous
page from 'uncached_readdir'.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index c66fdb7..29d504d 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -401,6 +401,7 @@
 #endif /* CONFIG_NFS_V3 */
 extern const struct file_operations nfs_file_operations;
 extern const struct address_space_operations nfs_file_aops;
+extern const struct address_space_operations nfs_dir_aops;
 
 static inline struct nfs_open_context *nfs_file_open_context(struct file *filp)
 {