netdev - Re: [PATCH] netfilter: per-cpu spin-lock with recursion (v0.8)

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Date:	Fri, 17 Apr 2009 07:55:37 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	paulmck@...ux.vnet.ibm.com, David Miller <davem@...emloft.net>,
	kaber@...sh.net, torvalds@...ux-foundation.org,
	dada1@...mosbay.com, jeff.chua.linux@...il.com, paulus@...ba.org,
	mingo@...e.hu, laijs@...fujitsu.com, jengelh@...ozas.de,
	r000n@...0n.net, linux-kernel@...r.kernel.org,
	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
	benh@...nel.crashing.org
Subject: Re: [PATCH] netfilter: per-cpu spin-lock with recursion (v0.8)

On Thu, 2009-04-16 at 16:52 -0700, Stephen Hemminger wrote:

>   - Lockdep doesn't really handle this well

> +/**
> + * xt_table_info_lock_all - lock xt table info for update
> + *
> + * Locks out all readers, and blocks bottom half
> + */
> +void xt_table_info_lock_all(void)
> +{
> +	int i;
> +
> +	local_bh_disable();
> +	for_each_possible_cpu(i) {
> +		struct xt_lock *lock = &per_cpu(xt_info_locks, i);
> +		spin_lock(&lock->lock);
> +		BUG_ON(lock->depth != -1);
> +	}
> +}
> +EXPORT_SYMBOL_GPL(xt_table_info_lock_all);

Quite so, this is the old MAX_LOCK_DEPTH < NR_CPUS issue for large
systems.

Last time this came up David found another way of solving the problem.
Not having fully read this thread, I cannot suggest one myself -- except
that RCU domains as suggested by David sound good.



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