From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754658AbaHALSY (ORCPT ); Fri, 1 Aug 2014 07:18:24 -0400 Received: from mail-qa0-f42.google.com ([209.85.216.42]:44246 "EHLO mail-qa0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751008AbaHALSX (ORCPT ); Fri, 1 Aug 2014 07:18:23 -0400 From: Jianyu Zhan To: tj@kernel.org, gregkh@linuxfoundation.org Cc: linux-kernel@vger.kernel.org, nasa4836@gmail.com, Jianyu Zhan Subject: [PATCH RFC] sysfs: fix the race of "parent deleted before child added" Date: Fri, 1 Aug 2014 19:18:12 +0800 Message-Id: <1406891892-10992-1-git-send-email-nasa4836@gmail.com> X-Mailer: git-send-email 2.0.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jianyu Zhan I've met such a race conditon the same as what commit 3a198886 ("sysfs: handle 'parent deleted before child added'") tackled. The senario got triggered under a torturing test of quick disk removal and plugging. The forementioned commit 3a198886 didn't really fix this race, it just narrows down the racy window. A proper fix for this is to pin the parent kernfs_node on the dir_entry creation point (sysfs_create_dir_ns), and to de-pin the parent on the dir_entry deletion point(sysfs_remove_dir). Though Tejun has added a comment in sysfs_remove_dir to warn such a race and leave the option to upper layer. But wrt correct logic point, I think it is good to add such pin behavior. Note. another commit 26ea12de("kobject: grab an extra reference on kobject->sd to allow duplicate deletes") also adds such a pin at the kobject layer. But this commit tackles different issue - it pins an entry(not its parent) after its creation, to allow duplicate deletions. Signed-off-by: Jianyu Zhan --- fs/sysfs/dir.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c index 0b45ff4..0ac82cd 100644 --- a/fs/sysfs/dir.c +++ b/fs/sysfs/dir.c @@ -49,7 +49,12 @@ int sysfs_create_dir_ns(struct kobject *kobj, const void *ns) else parent = sysfs_root_kn; - if (!parent) + /* + * We might race with the parent node removal. + * To avoid such race and for logic correctness, + * we pin the parent node here. + */ + if (!sysfs_get(parent)) return -ENOENT; kn = kernfs_create_dir_ns(parent, kobject_name(kobj), @@ -94,6 +99,10 @@ void sysfs_remove_dir(struct kobject *kobj) if (kn) { WARN_ON_ONCE(kernfs_type(kn) != KERNFS_DIR); + /* + * Drop our pin on parent + */ + sysfs_put(kn->parent); kernfs_remove(kn); } } -- 2.0.1.472.g6f92e5f