lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20120201162851.GD6731@somewhere.redhat.com>
Date:	Wed, 1 Feb 2012 17:28:55 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Li Zefan <lizf@...fujitsu.com>, Tejun Heo <tj@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mandeep Singh Baines <msb@...omium.org>,
	Containers <containers@...ts.linux-foundation.org>,
	Cgroups <cgroups@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Paul Menage <paul@...lmenage.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: Q: cgroup: Questions about possible issues in cgroup locking

On Wed, Dec 21, 2011 at 02:08:48PM +0100, Oleg Nesterov wrote:
> On 12/21, Frederic Weisbecker wrote:
> > - Is the check for use_task_css_set_links in cgroup_post_fork() safe? given
> > it is checked outside css_set_lock?
> >
> > Imagine this:
> >
> > CPU 0                                                        CPU 1
> > ----                                                         -----
> >
> > cgroup_enable_task_cg() {
> > 	uset_tasks_css_set_links = 1
> > 	for_each_thread() {
> > 		add tasks in the list
> > 	}
> > }
> >                                                            do_fork() {
> >                                                                cgroup_post_fork() {
> >                                                                      use_tasks_css_set_links appears
> >                                                                      to be equal to 0 due to write/read
> >                                                                       not flushed. New task won't
> >                                                                       appear to the list.
> 
> Yes, I was thinking about this too.
> 
> Or (I think) they can race "contrariwise". CPU_1 creates the new child,
> then CPU_0 sets uset_tasks_css_set_links = 1. But afaics there is no any
> guarantee that CPU_0 sees the result of list_add_tail_rcu().

Exactly! In fact even if RCU was safe with while_each_thread() it wouldn't
be enough for us because of that.

I fear we need the read_lock(tasklist_lock) here, with a pair of smp
barriers to ensure use_task_css_set_links update is visible as
expected.

I'll try to cook something.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ