From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758402Ab3GZJ4X (ORCPT ); Fri, 26 Jul 2013 05:56:23 -0400 Received: from smtpbg63.qq.com ([103.7.29.150]:56915 "HELO smtpbg63.qq.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1758360Ab3GZJ4U (ORCPT ); Fri, 26 Jul 2013 05:56:20 -0400 X-QQ-mid: bizesmtp1t1374832575t659t198 X-QQ-SSF: 01400000000000F0FPF2000A0000000 Message-ID: <51F24864.7070306@tnsoft.com.cn> Date: Fri, 26 Jul 2013 17:59:00 +0800 From: Dennis Chen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 To: linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org CC: Tejun Heo , xiyou.wangcong@gmail.com, Dennis Chen Subject: Re: [PATCH] race condition fixing in sysfs_create_dir References: <51F24612.6030509@tnsoft.com.cn> In-Reply-To: <51F24612.6030509@tnsoft.com.cn> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/26/2013 05:49 PM, Dennis Chen wrote: > The patch is trying its best to avoid creating a dir under a parent dir which is removing from > the system: > PATH0 (create a dir under 'PARENT/...') PATH1 (remove the 'PARENT/...') > sysfs_create_dir() { sysfs_remove_dir() { > ... ... > if (kobj->parent) spin_lock(&sysfs_assoc_lock); > parent_sd = kobj->parent->sd; <----- kobj->sd = NULL; > else spin_unlock(&sysfs_assoc_lock); > parent_sd = &sysfs_root; > Suppose PATH1 enter the critical section first, then PATH0 begin to execute before kobj->sd > has been reset to NULL, possibly PATH0 will get a non-NULL parent_sd since lack of the > sysfs_assoc_lock protection in PATH0. In this case, PATH0 think it has a valid parent_sd which > can be freed by PATH1 in the followed, refer to the comments in the patch. Maybe we need > to figure out a perfect solution to solve the race condition, although the codes in question are > in slow path... > Signed-off-by: Dennis Chen > Cc: Greg Kroah-Hartman > Cc: Tejun Heo should be Tejun Heo > Cc: Wang Cong > --- > 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 e068e74..114073d 100644 > --- a/fs/sysfs/dir.c > +++ b/fs/sysfs/dir.c > @@ -746,13 +746,22 @@ int sysfs_create_dir(struct kobject * kobj) > BUG_ON(!kobj); > + spin_lock(&sysfs_assoc_lock); > if (kobj->parent) > parent_sd = kobj->parent->sd; > else > parent_sd = &sysfs_root; > - if (!parent_sd) > + if (!parent_sd) { > + spin_unlock(&sysfs_assoc_lock); > return -ENOENT; > + } > + spin_unlock(&sysfs_assoc_lock); > + /* TODO: although the sysfs is in a slow path, but in the operation > + * followed, we still have a window to let the sysfs_remove_dir to > + * free the memory space pointered by parent_sd till we inc its ref > + * count in __sysfs_add_one() > + */ > if (sysfs_ns_type(parent_sd)) > ns = kobj->ktype->namespace(kobj); Re CC Tejun whose email addess <@suse.de> is obsolete :)