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

[Will Deacon]

On Fri, Feb 05, 2016 at 01:25:47PM -0800, Shi, Yang wrote:
> 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.

I quite liked the sigtrap consolidation in my earlier (broken) approach.
Does the following work for you?

Will

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