netdev - Re: [PATCH] netfilter: use per-cpu recursive lock (v11)

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Date:	Tue, 21 Apr 2009 11:41:35 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Stephen Hemminger <shemminger@...tta.com>
CC:	Paul Mackerras <paulus@...ba.org>, paulmck@...ux.vnet.ibm.com,
	Eric Dumazet <dada1@...mosbay.com>,
	Evgeniy Polyakov <zbr@...emap.net>,
	David Miller <davem@...emloft.net>, kaber@...sh.net,
	torvalds@...ux-foundation.org, jeff.chua.linux@...il.com,
	mingo@...e.hu, jengelh@...ozas.de, r000n@...0n.net,
	linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
	netdev@...r.kernel.org, benh@...nel.crashing.org,
	mathieu.desnoyers@...ymtl.ca
Subject: Re: [PATCH] netfilter: use per-cpu recursive lock (v11)

Stephen Hemminger wrote:
> +/**
> + * xt_table_info_rdlock_bh - recursive read lock for xt table info
> + *
> + * Table processing calls this to hold off any changes to table
> + * (on current CPU). Always leaves with bottom half disabled.
> + * If called recursively, then assumes bh/preempt already disabled.
> + */
> +void xt_info_rdlock_bh(void)
> +{
> +	struct xt_info_lock *lock;
> +
> +	preempt_disable();
> +	lock = &__get_cpu_var(xt_info_locks);
> +	if (likely(++lock->depth == 0))

Maybe I missed something. I think softirq may be still enabled here.
So what happen when xt_info_rdlock_bh() called recursively here?

> +		spin_lock_bh(&lock->lock);
> +	preempt_enable_no_resched();
> +}
> +EXPORT_SYMBOL_GPL(xt_info_rdlock_bh);
> +

Is this OK for you:

void xt_info_rdlock_bh(void)
{
	struct xt_info_lock *lock;

	local_bh_disable();
	lock = &__get_cpu_var(xt_info_locks);
	if (likely(++lock->depth == 0))
		spin_lock(&lock->lock);
}

Lai.

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