linux-kernel - Re: [mm][RFC][PATCH 0/11] mm accessor updates.

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Message-ID: <alpine.DEB.2.00.0912171412040.4640@router.home>
Date:	Thu, 17 Dec 2009 14:13:42 -0600 (CST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Andi Kleen <andi@...stfloor.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mingo@...e.hu" <mingo@...e.hu>, minchan.kim@...il.com
Subject: Re: [mm][RFC][PATCH 0/11] mm accessor updates.

On Thu, 17 Dec 2009, Peter Zijlstra wrote:

> > You always need some reference on the mm_struct (mm_read_lock) if you are
> > going to sleep to ensure that mm_struct still exists after waking up (page
> > fault, page allocation). RCU and other spin locks are not helping there.
>
> Depends what you go to sleep for, the page fault retry patches simply
> retook the whole fault and there is no way the mm could have gone away
> when userspace isn't executing.

get_user_pages ?

> Also pinning a page will pin the vma will pin the mm, and then you can
> always take explicit mm_struct refs, but you really want to avoid that
> since that's a global cacheline again.

Incrementing a refcount on some random page wont protect you unless
mmap_sem is held.

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