netdev - Re: [PATCH 2/2] udp: RCU handling for Unicast packets.

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Message-Id: <1225365126.7803.66.camel@twins>
Date:	Thu, 30 Oct 2008 12:12:06 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	Corey Minyard <minyard@....org>,
	David Miller <davem@...emloft.net>, shemminger@...tta.com,
	benny+usenet@...rsen.dk, netdev@...r.kernel.org,
	paulmck@...ux.vnet.ibm.com,
	Christoph Lameter <cl@...ux-foundation.org>,
	johnpol@....mipt.ru, Christian Bell <christian@...i.com>
Subject: Re: [PATCH 2/2] udp: RCU handling for Unicast packets.

On Wed, 2008-10-29 at 15:36 +0100, Eric Dumazet wrote:
> +/**
> + * hlist_for_each_entry_rcu_safenext - iterate over rcu list of given type
> + * @tpos:      the type * to use as a loop cursor.
> + * @pos:       the &struct hlist_node to use as a loop cursor.
> + * @head:      the head for your list.
> + * @member:    the name of the hlist_node within the struct.
> + * @next:       the &struct hlist_node to use as a next cursor
> + *
> + * Special version of hlist_for_each_entry_rcu that make sure
> + * each next pointer is fetched before each iteration.
> + */
> +#define hlist_for_each_entry_rcu_safenext(tpos, pos, head, member, next) \
> +       for (pos = rcu_dereference((head)->first);                       \
> +               pos && ({ next = pos->next; smp_rmb(); prefetch(next); 1; }) && \
> +               ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; }); \
> +               pos = rcu_dereference(next))
> +

why _safenext and not _safe like hlist_for_each_entry_safe() which also
keeps a next pointer?

Also note the difference in argument order between these two.

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