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

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Message-ID: <20090825181019.GT14722@random.random>
Date:	Tue, 25 Aug 2009 20:10:19 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Hugh Dickins <hugh.dickins@...cali.co.uk>
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 Tue, Aug 25, 2009 at 06:49:09PM +0100, Hugh Dickins wrote:
> Sorry, I just don't get it.  How does down_read here help?
> Perhaps you thought ksm.c had down_write of mmap_sem in all cases?
> 
> No, and I don't think we want to change its down_reads to down_writes.

Looking ksm.c it should have been down_write indeed...

> Nor do we want to change your down_read here to down_write, that will
> just reintroduce the OOM deadlock that 9/12 was about solving.

I'm not sure anymore I get what this fix is about... mm_users is
allowed to go to 0. If mm_users is allowed to go to 0, it's up to ksm
to check inside its inner loops that mm_users is 0 and bail
out. Bailing out it will unblock exit so that exit_mmap can run. What
exactly is the unfixable issue?
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