linux-kernel - Re: [patch 1/6] mmu

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Date:	Wed, 30 Jan 2008 18:10:32 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrea Arcangeli <andrea@...ranet.com>
Cc:	Christoph Lameter <clameter@....com>, Robin Holt <holt@....com>,
	Avi Kivity <avi@...ranet.com>, Izik Eidus <izike@...ranet.com>,
	Nick Piggin <npiggin@...e.de>, kvm-devel@...ts.sourceforge.net,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	steiner@....com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com, Hugh Dickins <hugh@...itas.com>
Subject: Re: [patch 1/6] mmu_notifier: Core code


On Wed, 2008-01-30 at 16:37 +0100, Andrea Arcangeli wrote:
> On Tue, Jan 29, 2008 at 06:29:10PM -0800, Christoph Lameter wrote:
> > +void mmu_notifier_release(struct mm_struct *mm)
> > +{
> > +	struct mmu_notifier *mn;
> > +	struct hlist_node *n, *t;
> > +
> > +	if (unlikely(!hlist_empty(&mm->mmu_notifier.head))) {
> > +		rcu_read_lock();
> > +		hlist_for_each_entry_safe_rcu(mn, n, t,
> > +					  &mm->mmu_notifier.head, hlist) {
> > +			hlist_del_rcu(&mn->hlist);
> 
> This will race and kernel crash against mmu_notifier_register in
> SMP. You should resurrect the per-mmu_notifier_head lock in my last
> patch (except it can be converted from a rwlock_t to a regular
> spinlock_t) and drop the mmap_sem from
> mmu_notifier_register/unregister.

Agreed, sorry for this oversight.

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