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