Date: Thu, 31 Jan 2008 14:32:35 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Oleg Nesterov <oleg@tv-sign.ru>, ebiederm@xmission.com,
       paulmck@linux.vnet.ibm.com, xemul@openvz.org,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fix tasklist + find_pid() with CONFIG_PREEMPT_RCU
Message-ID: <20080131133235.GD8499@elte.hu>
References: <20080129164019.GA2060@tv-sign.ru> <20080129150209.663538cb.akpm@linux-foundation.org>
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* Andrew Morton <akpm@linux-foundation.org> wrote:

> On Tue, 29 Jan 2008 19:40:19 +0300
> Oleg Nesterov <oleg@tv-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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