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

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Date:	Sat, 18 Sep 2010 03:29:39 +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:
>
> Instead, this change implements the more complex option two.  It
> migrates the ____call_usermodehelper() thread into the same namespaces
> as the dumping process.  It does not assign a pid in that namespace so
> the collector will appear to be pid 0.

Hmm... You mean, it won't visible in that namespace? Afacis, it should
have the correct pid in the init ns, no?

I am a bit worried task_active_pid_ns() != nsproxy->pid_ns, but perhaps
this is OK... Say, sys_getpid() returns 0, strange.

> +		/* Run the core_collector in the crashing namespaces */
> +		if (copy_namespaces_unattached(0, current,
> +			&pipe_params.nsproxy, &pipe_params.fs)) {
> +			printk(KERN_WARNING "%s failed to copy namespaces\n",
> +			       __func__);
> +			argv_free(helper_argv);
> +			goto fail_dropcount;
> +		}

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.

In fact, I do not understand why create_new_namespaces() is used. It
is called with flags == 0 anyway, can't we just do

	ns = coredumping_task->nsproxy;
	get_nsproxy(ns);	
	switch_task_namespaces(current, ns);

?

Oleg.

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