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Date: Thu, 17 Apr 2008 21:08:44 +0400
From: Oleg Nesterov <oleg@tv-sign.ru>
To: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Paul Menage <menage@google.com>, Andrew Morton <akpm@linux-foundation.org>,
       serue@us.ibm.com, penberg@cs.helsinki.fi, linux-kernel@vger.kernel.org
Subject: Re: [Fwd: [-mm] Add an owner to the mm_struct (v9)]
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References: <48036677.3010807@linux.vnet.ibm.com> <20080414170709.736819b6.akpm@linux-foundation.org> <20080415171359.GA352@tv-sign.ru> <6599ad830804151113i73010bb4x48e658195f295d41@mail.gmail.com> <20080415195950.GA113@tv-sign.ru> <4806C633.3000302@linux.vnet.ibm.com> <20080417113000.GB103@tv-sign.ru> <6599ad830804170934i6df9fe42kd979492babe03be@mail.gmail.com> <20080417161936.GB4482@tv-sign.ru> <48078B9B.9070508@linux.vnet.ibm.com>
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On 04/17, Balbir Singh wrote:
> 
> Oleg Nesterov wrote:
> >> CLONE_THREAD without CLONE_VM when creating a new subthread.
> > 
> > No, no, this is not possible/allowed.
> > 
> > Please look at copy_process, CLONE_THREAD requires CLONE_SIGHAND,
> > CLONE_SIGHAND needs CLONE_VM.
> > 
> 
> What about the other way round, CLONE_VM without CLONE_THREAD?

Yes, this is possible, and this is why mm_update_next_owner() has to be so
complicated. The same for zap_threads/elf_core_dump.

If only I knew why we allow CLONE_VM! except for CLONE_THREAD/CLONE_VFORK
of course, but there are trivial.


And thanks to you and Paul for your explanations.

Oleg.