linux-kernel - Re: [RFC] mlock/stack guard interaction fixup

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Message-ID: <19570.38608.79434.179797@chiark.greenend.org.uk>
Date:	Mon, 23 Aug 2010 16:42:08 +0100
From:	ijackson@...ark.greenend.org.uk
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Greg KH <gregkh@...e.de>, Ian Campbell <ijc@...lion.org.uk>,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	stable-review@...nel.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Peter Zijlstra <peterz@...radead.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [RFC] mlock/stack guard interaction fixup

Linus Torvalds writes ("Re: [RFC] mlock/stack guard interaction fixup"):
> Although you do need to have some really odd things going on for any
> of them to make any difference. Notably, you need to do mlock or
> mprotect on the stack segment, which no sane program does.

mlocking the stack is entirely sensible and normal for a real-time
program.  Most such programs use mlockall but there is no particular
reason why a program that has some more specific requirements should
use mlock to lock only a part of the stack.  (Perhaps it has only one
real-time thread?)

Locking, including of the stack, is discussed extensively here:
  http://www.opengroup.org/onlinepubs/9699919799/xrat/V4_xsh_chap02.html
  section "Memory locking functions" subsection "Requirements".

Ian.

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