linux-kernel - Re: [PATCH] 3/4 combine RCU with seqlock to allow mmu notifier methods to sleep (#v9 was 1/4)

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Date:	Fri, 07 Mar 2008 17:52:42 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrea Arcangeli <andrea@...ranet.com>
Cc:	Christoph Lameter <clameter@....com>,
	Jack Steiner <steiner@....com>, Nick Piggin <npiggin@...e.de>,
	akpm@...ux-foundation.org, Robin Holt <holt@....com>,
	Avi Kivity <avi@...ranet.com>, kvm-devel@...ts.sourceforge.net,
	general@...ts.openfabrics.org,
	Steve Wise <swise@...ngridcomputing.com>,
	Roland Dreier <rdreier@...co.com>,
	Kanoj Sarcar <kanojsarcar@...oo.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com
Subject: Re: [PATCH] 3/4 combine RCU with seqlock to allow mmu notifier
	methods to sleep (#v9 was 1/4)

On Fri, 2008-03-07 at 16:23 +0100, Andrea Arcangeli wrote:


> @@ -42,11 +45,19 @@ int __mmu_notifier_clear_flush_young(str
>  	struct mmu_notifier *mn;
>  	struct hlist_node *n;
>  	int young = 0;
> +	unsigned seq;
>  
>  	rcu_read_lock();
> +restart:
> +	seq = read_seqbegin(&mm->mmu_notifier_lock);
>  	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_list, hlist) {
> -		if (mn->ops->clear_flush_young)
> +		if (mn->ops->clear_flush_young) {

hlist_del_rcu(&mn->hlist)

> +			rcu_read_unlock();

kfree(mn);

>  			young |= mn->ops->clear_flush_young(mn, mm, address);

*BANG*

> +			rcu_read_lock();
> +		}
> +		if (read_seqretry(&mm->mmu_notifier_lock, seq))
> +			goto restart;
>  	}
>  	rcu_read_unlock();



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