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From: David Howells <dhowells@redhat.com>
To: paulmck@linux.vnet.ibm.com
Cc: dhowells@redhat.com, linux-kernel@vger.kernel.org, mingo@elte.hu,
	laijs@cn.fujitsu.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
	josh@joshtriplett.org, dvhltc@us.ibm.com, niv@us.ibm.com,
	tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org,
	Valdis.Kletnieks@vt.edu, eric.dumazet@gmail.com
Subject: Re: [PATCH tip/urgent] rcu: add rcu_access_pointer and rcu_dereference_protected
Date: Wed, 07 Apr 2010 18:20:48 +0100	[thread overview]
Message-ID: <27837.1270660848@redhat.com> (raw)
In-Reply-To: <20100407171342.GF2481@linux.vnet.ibm.com>

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

> In other cases, there will be a reference counter or a "not yet fully
> initialized" flag that can (and should) be tested.

Why would you be using rcu_access_pointer() there?  Why wouldn't you be using
rcu_dereference_protected()?


Also, one other thing:  Should the default versions of these functions make
some reference to 'c' to prevent compiler warnings?  Should:

	#define rcu_dereference_check(p, c)	rcu_dereference_raw(p)

for example, be:

	#define rcu_dereference_check(p, c)	\
	({					\
		if (1 || !(c))			\
			rcu_dereference_raw(p);	\
	})

I'm not sure it's necessary, but it's possible to envisage a situation where
someone calculates something specifically for use in 'c', which will cause an
warning from the compiler if c isn't then checked.

David

  parent reply	other threads:[~2010-04-07 17:21 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-04-07 16:26 [PATCH tip/urgent] rcu: add rcu_access_pointer and rcu_dereference_protected Paul E. McKenney
2010-04-07 16:38 ` Eric Dumazet
2010-04-07 16:45 ` Mathieu Desnoyers
2010-04-07 17:00 ` David Howells
2010-04-07 17:13   ` Paul E. McKenney
2010-04-07 17:20   ` David Howells [this message]
2010-04-07 23:00     ` Paul E. McKenney
2010-04-08 16:46       ` Paul E. McKenney
2010-04-08 19:04       ` David Howells
2010-04-08 19:53         ` Paul E. McKenney

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