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Date: Sat, 5 Apr 2008 02:57:59 +0200
From: Andrea Arcangeli <andrea@qumranet.com>
To: Christoph Lameter <clameter@sgi.com>
Cc: Robin Holt <holt@sgi.com>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
       kvm-devel@lists.sourceforge.net,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, general@lists.openfabrics.org,
       steiner@sgi.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [patch 02/10] emm: notifier logic
Message-ID: <20080405005759.GH14784@duo.random>
References: <20080404223048.374852899@sgi.com> <20080404223131.469710551@sgi.com>
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On Fri, Apr 04, 2008 at 03:30:50PM -0700, Christoph Lameter wrote:
> +	mm_lock(mm);
> +	e->next = mm->emm_notifier;
> +	/*
> +	 * The update to emm_notifier (e->next) must be visible
> +	 * before the pointer becomes visible.
> +	 * rcu_assign_pointer() does exactly what we need.
> +	 */
> +	rcu_assign_pointer(mm->emm_notifier, e);
> +	mm_unlock(mm);

My mm_lock solution makes all rcu serialization an unnecessary
overhead so you should remove it like I already did in #v11. If it
wasn't the case, then mm_lock wouldn't be a definitive fix for the
race.

> +		e = rcu_dereference(e->next);

Same here.

From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrea Arcangeli <andrea@qumranet.com>
Subject: [ofa-general] Re: [patch 02/10] emm: notifier logic
Date: Sat, 5 Apr 2008 02:57:59 +0200
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	<20080404223131.469710551@sgi.com>
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Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, kvm-devel@lists.sourceforge.net,
	steiner@sgi.com, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, Robin Holt <holt@sgi.com>,
	general@lists.openfabrics.org,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Christoph Lameter <clameter@sgi.com>
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On Fri, Apr 04, 2008 at 03:30:50PM -0700, Christoph Lameter wrote:
> +	mm_lock(mm);
> +	e->next = mm->emm_notifier;
> +	/*
> +	 * The update to emm_notifier (e->next) must be visible
> +	 * before the pointer becomes visible.
> +	 * rcu_assign_pointer() does exactly what we need.
> +	 */
> +	rcu_assign_pointer(mm->emm_notifier, e);
> +	mm_unlock(mm);

My mm_lock solution makes all rcu serialization an unnecessary
overhead so you should remove it like I already did in #v11. If it
wasn't the case, then mm_lock wouldn't be a definitive fix for the
race.

> +		e = rcu_dereference(e->next);

Same here.