linux-kernel - Re: [-mm] Add an owner to the mm

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Date:	Fri, 28 Mar 2008 07:06:52 -0700
From:	"Paul Menage" <menage@...gle.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	"Pavel Emelianov" <xemul@...nvz.org>,
	"Hugh Dickins" <hugh@...itas.com>,
	"Sudhir Kumar" <skumar@...ux.vnet.ibm.com>,
	"YAMAMOTO Takashi" <yamamoto@...inux.co.jp>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, taka@...inux.co.jp,
	linux-mm@...ck.org, "David Rientjes" <rientjes@...gle.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [-mm] Add an owner to the mm_struct (v2)

On Fri, Mar 28, 2008 at 5:54 AM, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
>
>  Thinking more, I don't think it makes sense for us to overload task_lock() to do
>  the mm->owner handling (we don't want to mix lock domains). task_lock() is used
>  for several things
>
>  1. We don't want to make task_lock() rules more complicated by having it protect
>  an mm member to save space
>  2. We don't want more contention on task_lock()
>

This isn't to save space, it's to provide correctness. We *have* to
hold task_lock(new_owner) before setting mm->owner = new_owner,
otherwise we have no guarantee that new_owner is still a user of mm.

Paul
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