linux-kernel - Re: [RFC][PATCH 11/18] sched: Add p->pi_lock to task_rq

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Date:	Thu, 03 Feb 2011 09:49:13 -0800
From:	Frank Rowand <frank.rowand@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Chris Mason <chris.mason@...cle.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <efault@....de>,
	Oleg Nesterov <oleg@...hat.com>, Paul Turner <pjt@...gle.com>,
	Jens Axboe <axboe@...nel.dk>,
	Yong Zhang <yong.zhang0@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 11/18] sched: Add p->pi_lock to task_rq_lock()

On 02/03/11 09:16, Peter Zijlstra wrote:
> On Fri, 2011-01-28 at 16:21 -0800, Frank Rowand wrote:
>> On 01/04/11 06:59, Peter Zijlstra wrote:

< snip >

>>> @@ -2646,9 +2647,9 @@ void sched_fork(struct task_struct *p, i
>>>          *
>>>          * Silence PROVE_RCU.
>>>          */
>>> -       rcu_read_lock();
>>> +       raw_spin_lock_irqsave(&p->pi_lock, flags);
>>>         set_task_cpu(p, cpu);
>>> -       rcu_read_unlock();
>>> +       raw_spin_unlock_irqrestore(&p->pi_lock, flags);
>>
>> Does "* Silence PROVE_RCU." no longer apply after remove rcu_read_lock() and
>> rcu_read_unlock()?
> 
> I think the locking is still strictly superfluous, I can't seem to
> recollect why I changed it from RCU to pi_lock, but since the task is
> fresh and unhashed it really cannot be subject to concurrency.

Sorry, my comment was not very clear.  I meant to ask: should the
comment "* Silence PROVE_RCU." also be removed?

-Frank
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