linux-kernel - Re: [PATCH tip/core/rcu 0/21] v6 add lockdep-based diagnostics to rcu

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Message-Id: <201002231359.07910.arnd@arndb.de>
Date:	Tue, 23 Feb 2010 13:59:07 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	paulmck@...ux.vnet.ibm.com
Cc:	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,
	dhowells@...hat.com
Subject: Re: [PATCH tip/core/rcu 0/21] v6 add lockdep-based diagnostics to rcu_dereference()

On Tuesday 23 February 2010, Paul E. McKenney wrote:
> This patch series adds lockdep-based checking to the rcu_dereference()
> primitive in order to flag misuses of RCU.

While I haven't looked much at this series, I've been thinking about
adding static diagnostics for rcu_dereference misuse, in the form of
an __rcu address space qualifier for pointers. Such a patch would
obviously conflict with this series, so I'd wait for yours to go
in first, but maybe you like the idea enough to do it yourself ;-).

The observation is that all accesses to an RCU protected pointer
are either through rcu_dereference, rcu_assign_pointer or one of their
variants. so it should be possible to add a new address space like we
have for __iomem, __user and soon __percpu and have sparse check that
we use RCU consistently on pointers that need it.

	Arnd
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