linux-kernel - Re: [patch 5/5] elf: Add support for loading ET

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Date:	Fri, 14 Oct 2011 10:33:04 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	linux-kernel@...r.kernel.org, Andrew Vagin <avagin@...allels.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	James Bottomley <jbottomley@...allels.com>,
	Glauber Costa <glommer@...allels.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Daniel Lezcano <dlezcano@...ibm.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [patch 5/5] elf: Add support for loading ET_CKPT files

Hello, again.

On Fri, Oct 14, 2011 at 10:10:33AM -0700, Tejun Heo wrote:
> I see that you removed zapping to allow restoring multi-threaded
> process, which seems quite scary to me.  It might be okay, I don't
> know, but IMHO it just isn't a very good idea to introduce such
> variation to basic exec behavior for this rather narrow use case.

* It's still calling exec_mmap(), so the exec'ing thread will be on
  the new mm while other threads would still be on the old one.

* There are operations which assume that the calling task is
  de-threaded and thus has exclusive access to data structures which
  can be shared among the thread group (e.g. signal struct).  How are
  accesses to them synchronized?

* What about properties which should be reset and then shared by
  threads by inheriting (credentials, comm, self_exec_id and so on)?
  e.g. new thread follows exec-time imposed rules but old ones keep
  their original credentials.

So, no, it really doesn't look good.

Thanks.

-- 
tejun
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