linux-kernel - Re: [PATCH] fix tasklist + find_pid() with CONFIG_PREEMPT

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Date:	Wed, 30 Jan 2008 15:17:33 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Oleg Nesterov <oleg@...sign.ru>, ebiederm@...ssion.com,
	mingo@...e.hu, paulmck@...ux.vnet.ibm.com, xemul@...nvz.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fix tasklist + find_pid() with CONFIG_PREEMPT_RCU


On Tue, 2008-01-29 at 15:02 -0800, Andrew Morton wrote:
> On Tue, 29 Jan 2008 19:40:19 +0300
> Oleg Nesterov <oleg@...sign.ru> wrote:
> 
> > With CONFIG_PREEMPT_RCU read_lock(tasklist_lock) doesn't imply rcu_read_lock(),
> 
> I'm suspecting that we have other code which assumes that read_lock, write_lock
> and spin_lock imply rcu_read_lock().
> 
> I wonder if there are any sane runtime checks we can put in there to find
> such problems.

I have a lockdep annotation that finds rcu_dereference() usages outside
of rcu_read_lock().

Trouble is the amazing amount of output, I haven't come round to going
through it and annotation the false positives (think rcu safe library
routines called from contexts where the rcu capability is not used).



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