linux-kernel - Using sparse to catch invalid RCU dereferences?

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Date:	Tue, 08 Apr 2008 00:04:16 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	linux-sparse <linux-sparse@...r.kernel.org>
Subject: Using sparse to catch invalid RCU dereferences?

Hi,

Just a thought, I haven't tried this yet because I'm not entirely sure
it's actually correct. I was just thinking it should be possible to
introduce something like

	#define __rcu	__attribute__((address_space(3)))

(for sparse only, of course) and then be able to say

	struct myfoo *foo __rcu;

and sparse would warn on

	struct myfoo *bar = foo;

but not on

	struct myfoo *bar = rcu_dereference(foo);

by way of using __force inside rcu_dereference(), rcu_assign_pointer()
etc.

Would this be feasible? Or should one actually use __bitwise/__force to
also get the warning when assigning between two variables both marked
__rcu?

johannes

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