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SubjectRe: [PATCH 2/2] ptrace: fix set_task_blockstep()->update_debugctlmsr() logic
On 08/03, Sebastian Andrzej Siewior wrote:
>
> On 08/03/2012 06:29 PM, Oleg Nesterov wrote:
>> diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
>> index afa60db..636402e 100644
>> --- a/arch/x86/kernel/step.c
>> +++ b/arch/x86/kernel/step.c
>> @@ -166,12 +166,18 @@ static void set_task_blockstep(struct task_struct *task, bool on)
>> else
>> clear_tsk_thread_flag(task, TIF_BLOCKSTEP);
>>
>> + if (task != current)
>> + return;
>> +
>> + /* ensure irq/preemption can't change debugctl in between */
>> + local_irq_disable();
>> debugctl = get_debugctlmsr();
>> if (on)
>> debugctl |= DEBUGCTLMSR_BTF;
>> else
>> debugctl&= ~DEBUGCTLMSR_BTF;
>> 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?

Oleg.



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