linux-kernel - RE: [PATCH] rcu: fix a race in hlist_nulls_for_each_entry

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Message-ID: <AE90C24D6B3A694183C094C60CF0A2F6026B7242@saturn3.aculab.com>
Date:	Tue, 21 May 2013 14:42:34 +0100
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Roman Gushchin" <klamm@...dex-team.ru>
Cc:	"Dipankar Sarma" <dipankar@...ibm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	<zhmurov@...dex-team.ru>, <linux-kernel@...r.kernel.org>,
	<netdev@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>,
	"Eric Dumazet" <eric.dumazet@...il.com>,
	"Alexey Kuznetsov" <kuznet@....inr.ac.ru>,
	"James Morris" <jmorris@...ei.org>,
	"Hideaki YOSHIFUJI" <yoshfuji@...ux-ipv6.org>,
	"Patrick McHardy" <kaber@...sh.net>
Subject: RE: [PATCH] rcu: fix a race in hlist_nulls_for_each_entry_rcu macro

> >> -#define hlist_nulls_first_rcu(head) \
> >> -	(*((struct hlist_nulls_node __rcu __force **)&(head)->first))
> >> +#define hlist_nulls_first_rcu(head)			\
> >> +	(*((struct hlist_nulls_node __rcu __force **)	\
> >> +	   &((volatile typeof(*head) *)head)->first))
> >
> > I'd have thought it would be better to change hlist_nulls_first_rcu().
> 
> It's exactly what I suggest. May be I miss something? Please, clarify.

Gah - chasing through too many defines in too many header files!
Actually making the 'head' structure have volatile pointers
might be better.
Possibly in struct hlist_nulls_node itself.
There are toooo many casts for sanity :-)

	David



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