linux-kernel - Re: [PATCH] - support inheritance of mlocks across fork/exec V2

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Date:	Mon, 08 Dec 2008 15:33:05 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Lee Schermerhorn <Lee.Schermerhorn@...com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel <linux-kernel@...r.kernel.org>, riel@...hat.com,
	hugh@...itas.com, kosaki.motohiro@...fujitsu.com,
	linux-api@...r.kernel.org
Subject: Re: [PATCH] - support inheritance of mlocks across fork/exec V2

On Mon, 2008-12-08 at 16:05 -0500, Lee Schermerhorn wrote:
> > > In support of a "lock prefix command"--e.g., mlock <cmd>
> <args> ...
> > > Analogous to taskset(1) for cpu affinity or numactl(8) for numa memory
> > > policy.
> > > 
> > > Together with patches to keep mlocked pages off the LRU, this will
> > > allow users/admins to lock down applications without modifying them,
> > > if their RLIMIT_MEMLOCK is sufficiently large, keeping their pages
> > > off the LRU and out of consideration for reclaim.
> > > 
> > > Potentially useful, as well, in real-time environments to force
> > > prefaulting and residency for applications that don't mlock themselves.

This is a bit scary to me. Privilege and mode inheritance across
processes is the root of many nasty surprises, security and otherwise. 

Here's a crazy alternative: add a flag to containers instead? I think
this is a better match to what you're trying to do and will keep people
from being surprised when an mlockall call in one thread causes a
fork/exec in another thread to crash their box, but only sometimes.

-- 
Mathematics is the supreme nostalgia of our time.

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