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Date: Fri, 03 Aug 2012 20:28:14 +0200
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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To: Oleg Nesterov <oleg@redhat.com>
CC: Ingo Molnar <mingo@elte.hu>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        Anton Arapov <anton@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Roland McGrath <roland@hack.frob.com>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] ptrace: fix set_task_blockstep()->update_debugctlmsr()
 logic
References: <20120803162954.GA19806@redhat.com> <501BFF95.8040202@linutronix.de> <20120803173830.GA22687@redhat.com>
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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