linux-kernel - Re: [PATCH 2/2] exec: move core_pattern pipe helper into the crashing namespace

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Message-ID: <20100920185001.GA955@redhat.com>
Date:	Mon, 20 Sep 2010 20:50:01 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Will Drewry <wad@...omium.org>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Roland McGrath <roland@...hat.com>,
	Neil Horman <nhorman@...driver.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	containers@...ts.linux-foundation.org,
	Eugene Teo <eteo@...hat.com>, Tejun Heo <tj@...nel.org>,
	Serge Hallyn <serue@...ibm.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 2/2] exec: move core_pattern pipe helper into the
	crashing namespace

On 09/17, Will Drewry wrote:
>
> On Fri, Sep 17, 2010 at 8:29 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > This looks overcomplicated to me, or I missed something.
> >
> > I do not understand why should we do this beforehand, and why we need
> > copy_namespaces_unattached().
> >
> > Can't you just pass current to umh_pipe_setup() (or another helper) as
> > the argument? Then this helper can copy ->fs and ->nsproxy itself.
>
> I wasn't sure if it was reasonable to pass the current task_struct
> over, but I certainly can.

Why not? current calls call_usermodehelper_exec(), it can't go away
until subprocess_info->init() returns, it sleeps on wait_for_completion().

> In practice, this seems to amount to just adding a refcount to all the
> namespaces and creating a new nsproxy which isn't really needed.  Most
> likely, doing what you've suggested above plus the copy_fs_struct and
> the swap out will do the trick.  I'll try it out and see.  That's make
> it much clearer I think.

Yes, just get_nsproxy() (like fork() does) should be fine in this case.

As for copying ->fs, I am not sure actually. core_pattern is global,
say it is "|/coredumper". If you change ->root, then exec can fail
because that binary is not visible to the coredumping process?

Probably we should move core_pattern into ->pid_ns, I dunno.

Oleg.

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