linux-kernel - Re: [TOMOYO 05/15](repost) Domain transition handler functions.

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Message-Id: <1191417864.5599.2.camel@lappy>
Date:	Wed, 03 Oct 2007 15:24:24 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	jmorris@...ei.org, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, chrisw@...s-sol.org
Subject: Re: [TOMOYO 05/15](repost) Domain transition handler functions.


On Wed, 2007-10-03 at 22:04 +0900, Tetsuo Handa wrote:
> James Morris wrote:
> > I'm pretty sure that the singly linked list idea has been rejected a few 
> > times.  Just use the existing API.
> Too bad...
> 
> Well, is there a way to avoid read_lock when reading list?
> 
> Currently, TOMOYO Linux avoids read_lock, on the assumption that
> (1) First, ptr->next is initialized with NULL.
> (2) Later, ptr->next is assigned non-NULL address.
> (3) Assigning to ptr->next is done atomically.

 (4) wmb after asigning ptr->next
 (5) rmb before reading ptr->next

But please do look at the various rcu list primitives. RCU allows one to
avoid non-exclusive locks in many cases.

non-exclusive locks are evil, they must all die...

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