linux-kernel - Re: [PATCH 13/12] ksm: fix munlock during exit

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Message-ID: <Pine.LNX.4.64.0908262118470.4364@sister.anvils>
Date:	Wed, 26 Aug 2009 21:29:07 +0100 (BST)
From:	Hugh Dickins <hugh.dickins@...cali.co.uk>
To:	Andrea Arcangeli <aarcange@...hat.com>
cc:	Izik Eidus <ieidus@...hat.com>, Rik van Riel <riel@...hat.com>,
	Chris Wright <chrisw@...hat.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Justin M. Forbes" <jmforbes@...uxtx.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 13/12] ksm: fix munlock during exit_mmap deadlock

On Wed, 26 Aug 2009, Andrea Arcangeli wrote:
> On Wed, Aug 26, 2009 at 08:17:50PM +0100, Hugh Dickins wrote:
> > Has anyone looked at why Rawhide's mlockall is not faulting in the
> > pages, I wonder if there's a separate bug there?)
> 
> I reproduced only with self compiled mmotm kernel with full self
> compiled userland with just a mlockall and exit (not rawhide
> kernel/userland) so there's certainly no bug in rawhide, or at least
> nothing special about it.

I just tried again and got it myself: the faulting page is a PROT_NONE
page of libc, yes, that figures: mlocking would not fault it in, but
munlocking would (in its current implementation) insist on faulting it.

I don't know what my difficulty was yesterday: perhaps that page
isn't always PROT_NONE, perhaps I got confused and was testing the
wrong kernel, one without KSM or one with my follow_page munlock.

Hugh
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