mm/hwpoison: disable hwpoison filter during removing

hwpoison filter is enabled by hwpoison-inject module, after removing this
module, hwpoison filter still works.  What is worse, user can not find the
debugfs entries to know this.

Disable the hwpoison filter during removing hwpoison-inject module.

Link: https://lkml.kernel.org/r/20220509105641.491313-5-pizhenwei@bytedance.comSigned-off-by: zhenwei pi <pizhenwei@bytedance.com>
Acked-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/hwpoison-inject.c

@@ -65,6 +65,7 @@ DEFINE_DEBUGFS_ATTRIBUTE(unpoison_fops, NULL, hwpoison_unpoison, "%lli\n");
 
 static void pfn_inject_exit(void)
 {
+	hwpoison_filter_enable = 0;
 	debugfs_remove_recursive(hwpoison_dir);
 }