linux-kernel - Re: [PATCH tip/urgent] rcu: add rcu_access_pointer and rcu_dereference

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Message-ID: <27310.1270659627@redhat.com>
Date:	Wed, 07 Apr 2010 18:00:27 +0100
From:	David Howells <dhowells@...hat.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	dhowells@...hat.com, linux-kernel@...r.kernel.org, mingo@...e.hu,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, eric.dumazet@...il.com
Subject: Re: [PATCH tip/urgent] rcu: add rcu_access_pointer and rcu_dereference_protected

Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:

> The new rcu_access_pointer() primitive is for the case where the pointer
> is be fetch and not dereferenced.  This primitive may be used without
> protection, RCU or otherwise, due to the fact that it uses ACCESS_ONCE().
> ...
> +#define rcu_access_pointer(p, c) \

NAK.  This shouldn't have the conditional parameter 'c'.  Given that 'c' (by
analogy to rcu_dereference_check()) is there to describe the conditions under
which it's permitted to dereference the pointer, why is that relevant here?
What is it you're proving?

David
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