linux-kernel - Re: [PATCH] arm64: reenable interrupt when handling ptrace breakpoint

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Message-ID: <56969312.7070309@linaro.org>
Date:	Wed, 13 Jan 2016 10:10:26 -0800
From:	"Shi, Yang" <yang.shi@...aro.org>
To:	Will Deacon <will.deacon@....com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Catalin.Marinas@....com,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org, linux-rt-users@...r.kernel.org
Subject: Re: [PATCH] arm64: reenable interrupt when handling ptrace breakpoint

On 1/13/2016 9:23 AM, Will Deacon wrote:
> On Wed, Jan 13, 2016 at 09:17:46AM -0800, Shi, Yang wrote:
>> On 1/13/2016 2:26 AM, Will Deacon wrote:
>>> On Tue, Jan 12, 2016 at 11:59:54AM -0800, Shi, Yang wrote:
>>>> This might be buried in email storm during the holiday. Just want to double
>>>> check the status. I'm supposed there is no objection for getting it merged
>>>> in upstream?
>>>
>>> Sorry, when you replied with:
>>>
>>>> I think we could just extend the "signal delay send" approach from x86-64
>>>> to arm64, which is currently used by x86-64 on -rt kernel only.
>>>
>>> I understood that you were going to fix -rt, so I dropped this pending
>>> anything more from you.
>>>
>>> What's the plan?
>>
>> Sorry for the confusion. The "signal delay send" approach used by x86-64 -rt
>> should be not necessary for arm64 right now. Reenabling interrupt is still
>> the preferred approach.
>>
>> Since x86-64 has per-CPU IST exception stack, so preemption has to be
>> disabled all the time. However, it is not applicable to other architectures
>> for now, including arm64.
>
> Actually, we grew support for a separate IRQ stack in the recent merge
> window. Does that change things here, or are you referring to something
> else?

Had a quick look at the patches, it looks the irq stack is not nestable 
and it switches back to the original stack as long as irq handler is 
done before preempt happens. So, it sounds it won't change things here.

Thanks.,
Yang

>
> Will
>