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

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Message-ID: <56B5135B.3050801@linaro.org>
Date:	Fri, 5 Feb 2016 13:25:47 -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 10:10 AM, Shi, Yang wrote:
> 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.


Just had a quick test on 4.5-rc1. It survives with kgdbts, ptrace and 
ltp. So, it sounds safe with the "separate IRQ stack" change.

Thanks,
Yang

>
> Thanks.,
> Yang
>
>>
>> Will
>>
>