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

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Message-ID: <20080131133235.GD8499@elte.hu>
Date:	Thu, 31 Jan 2008 14:32:35 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Oleg Nesterov <oleg@...sign.ru>, ebiederm@...ssion.com,
	paulmck@...ux.vnet.ibm.com, xemul@...nvz.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fix tasklist + find_pid() with CONFIG_PREEMPT_RCU


* Andrew Morton <akpm@...ux-foundation.org> 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.

we usually caught them via the DEBUG_PREEMPT checks on PREEMPT_RT: stuff 
that has such implicit reliance tends to use smp_processor_id() along 
the way and that gets flagged if the non-preemptability guarantee of 
spin_lock() vanishes.

	Ingo
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