linux-kernel - Re: [Patch v4 1/2] freezer: check OOM kill while being frozen

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: <2606659.qXoKHWVyLl@vostro.rjw.lan>
Date:	Thu, 11 Sep 2014 01:38:21 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	Tejun Heo <tj@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>,
	Michal Hocko <mhocko@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Patch v4 1/2] freezer: check OOM kill while being frozen

On Wednesday, September 10, 2014 01:30:25 PM Cong Wang wrote:
> On Mon, Sep 8, 2014 at 4:29 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> > On Mon, Sep 8, 2014 at 4:42 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> >> On Monday, September 08, 2014 04:16:15 PM Cong Wang wrote:
> >>> On Mon, Sep 8, 2014 at 4:23 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> >>> >
> >>> > The reason why it matters for the suspend-time freezing is that we freeze tasks
> >>> > to take them out of the picture entirely until they are thawed.  Therefore we
> >>> > can't allow them to go back to the picture just for a while until they are
> >>> > killed.  Frozen tasks are not supposed to get back to the picture at all.
> >>> >
> >>>
> >>>
> >>> Ok, then checking TIF_MEMDIE is unsafe for PM freeze, we should
> >>> keep the cgroup_freezing() test to make sure freeze request is from
> >>> cgroup not PM. Question got answered. :)
> >>
> >> Do I think correctly that cgroups freezing and system suspend are
> >> mutually exclusive?  If not, then this still is problematic.
> >
> > Good point! Although rare, but it is possible we freeze a process both from
> > cgroup and PM. Hmm, this means we have to explicitly exclude PM rather
> > just checking cgroup freeze? Interesting, but I am not familiar with PM.
> >
> 
> I am wondering if the folllowing check makes any sense with regarding
> to rule out PM freeze:
> 
>         if ((!pm_nosig_freezing && !pm_freezing) &&
>             cgroup_freezing(current) && test_thread_flag(TIF_MEMDIE))
>                 return true;
> 
> PM will not freeze the process again if it is already frozen by cgroup,
> so here we just make sure that it will not thaw if PM freeze is in progress.
> 
> Am I missing anything?

And where exactly would you like to put this check?  Into __refrigerator()?

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
--
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/