linux-kernel - Re: [PATCH 2/2] ptrace: fix set_task_blockstep()->update

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Date:	Fri, 03 Aug 2012 20:28:14 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Roland McGrath <roland@...k.frob.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] ptrace: fix set_task_blockstep()->update_debugctlmsr()
 logic

On 08/03/2012 07:38 PM, Oleg Nesterov wrote:
>>>    	update_debugctlmsr(debugctl);
>>> +	local_irq_enable();
>>
>> wouldn't preempt_disable() be enough?
>
> preempt_disable() can't help if interrupt handler changes
> other bits in between?

So perf() uses this register as well. Since perf() uses the raw
primitives (raw_spin_lock()) shouldn't you do the same? If I recall
correctly (but it is Friday and late) local_irq_enable() wouldn't
disable irqs on RT and perf takes the raw lock so the irqs there should
be really disabled.

>
> Oleg.

Sebastian
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