linux-kernel - Re: [PATCH][BUGFIX] cgroups: fix pid namespace bug

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Message-ID: <20090702161548.GA13383@us.ibm.com>
Date:	Thu, 2 Jul 2009 11:15:49 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Paul Menage <menage@...gle.com>
Cc:	Li Zefan <lizf@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH][BUGFIX] cgroups: fix pid namespace bug

Quoting Paul Menage (menage@...gle.com):
> On Thu, Jul 2, 2009 at 6:26 AM, Serge E. Hallyn<serue@...ibm.com> wrote:
> > Quoting Li Zefan (lizf@...fujitsu.com):
> >> Paul Menage wrote:
> >> > On Wed, Jul 1, 2009 at 7:17 PM, Li Zefan<lizf@...fujitsu.com> wrote:
> >> >> But I guess we are going to fix the bug for 2.6.31? So is it ok to
> >> >> merge a new feature 'cgroup.procs' together into 2.6.31?
> >> >>
> >> >
> >> > Does this bug really need to be fixed for 2.6.31? I didn't think that
> >> > the namespace support in mainline was robust enough yet for people to
> >> > use them for virtual servers in production environments.
> >
> > I don't know where the bar is for 'production environments', but I'd
> > have to claim that pid namespaces are there...
> 
> Well, pid namespaces are marked as experimental, as are user
> namespaces (and were described as "very incomplete" a few months

incomplete (due to signaling issues which have mostly been resolved)
but stable and usable.

user namespace are a completely different story :)

> back). Pid namespaces are useful for process migration (which is still
> under development) or virtual servers (for which user namespaces are
> pretty much essential). So I'm not sure quite what you'd use pid
> namespaces for yet.

You don't need user namespaces to use pid namespaces for virtual
servers (depending on your use).

Now the fact remains this is a hard to trigger bug which doesn't
corrupt the kernel, and - to take back what I said earlier - userspace
can work around it by simply freezing the cgroup before reading its
tasks file.

So I guess I can go either way...  If Li's patch were more complicated
I'd definately be for waiting.  But I do object to the general process
of making a fix of a pretty bad bag depend on an unrelated new feature!

-serge
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