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References: <20091224182630.3DCB.A69D9226@jp.fujitsu.com> <1261647565.4937.177.camel@laptop>
From: Ulrich Drepper <drepper@gmail.com>
Date: Thu, 24 Dec 2009 09:15:47 -0800
Message-ID: <a36005b50912240915u48f326efh1d2c49980e79609c@mail.gmail.com>
Subject: Re: [PATCH] futex: Fix ZERO_PAGE cause infinite loop
To: Peter Zijlstra <peterz@infradead.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Hugh Dickins <hugh.dickins@tiscali.co.uk>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       Nick Piggin <npiggin@suse.de>, Ingo Molnar <mingo@elte.hu>,
       LKML <linux-kernel@vger.kernel.org>,
       Thomas Gleixner <tglx@linutronix.de>, Darren Hart <dvhltc@us.ibm.com>
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On Thu, Dec 24, 2009 at 01:39, Peter Zijlstra <peterz@infradead.org> wrote:
> What I mean is, all (?) futex ops assume userspace actually wrote
> something to the address in question to begin with, therefore it can
> never be the zero page.

In practice today this is likely always the case.  But it doesn't have
to be like that.  In theory a zero-initialized futex is a reasonable
object on which to wait.  You should not preclude this from happening
just because it's not done like this today.
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