Re: [PATCH 2/2] ptrace: fix set_task_blockstep()->update_debugctlmsr() logic

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 08/03/2012 06:29 PM, Oleg Nesterov wrote:
> --- 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();
>   }

I would say that you can remove this chunk. For task != current we
leave.
For uprobes we never set the bit, we only need it cleared. We get here
via int 3 and do_debug() already clears TIF_BLOCKSTEP because the
CPU clears the bit in CPU. So both, TIF_BLOCKSTEP and DEBUGCTLMSR_BTF
are never set.

Sebastian