linux-kernel - Re: [patch 01/15] Kernel Tracepoints

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Date:	Sat, 02 Aug 2008 02:03:57 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org,
	Masami Hiramatsu <mhiramat@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Hideo AOKI <haoki@...hat.com>,
	Takashi Nishiie <t-nishiie@...css.fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
Subject: Re: [patch 01/15] Kernel Tracepoints

On Fri, 2008-08-01 at 14:10 -0700, Paul E. McKenney wrote:

> Yeah, I was thinking in terms of rcu_dereference() working with both
> rcu_assign_pointer() and an as-yet-mythical rcu_assign_index().  Perhaps
> this would be a good time to get better names:
> 
> Current:	rcu_assign_pointer()	rcu_dereference()
> New Pointers:	rcu_publish_pointer()	rcu_subscribe_pointer()
> New Indexes:	rcu_publish_index()	rcu_subscribe_index()

Is it really worth the effort, splitting it out into these two cases?

> And, while I am at it, work in a way of checking for either being in
> the appropriate RCU read-side critical section and/or having the
> needed lock/mutex/whatever held -- something I believe PeterZ was
> prototyping some months back.

Yeah - I have (bitrotted a bit, but should be salvageable) lockdep
annotations for rcu_dereference().

The problem with them is the huge amount of false positives.. Take for
example the Radix tree code, its perfectly fine to use the radix tree
code without RCU - say you do the old rwlock style, still it uses
rcu_dereference().

I never figured out a suitable way to annotate that.

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