Re: [PATCH 15/20] ARM/hw_breakpoint: Convert to hotplug state machine

From	Thomas Gleixner <tglx@linutronix.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH 15/20] ARM/hw_breakpoint: Convert to hotplug state machine
Date	2016-11-18 14:50 +0100
Message-ID	<sERId-7NQ-5@gated-at.bofh.it> (permalink)
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On Fri, 18 Nov 2016, Will Deacon wrote:
> On Fri, Nov 18, 2016 at 02:11:58PM +0100, Thomas Gleixner wrote:
> > But it's guaranteed that cpuhp_setup_state() will not return before the
> > callback has been invoked on each online cpu.
> 
> Ok, that's good.
> 
> > If cpus are not yet online when that code is invoked, then it's the same
> > behaviour as before. It will be invoked when the cpu comes online.
> 
> Just to check, but what stops a CPU from coming online between the call
> to cpuhp_setup_state and the call to cpuhp_remove_state_nocalls in the
> case of failure (debug_err_mask isn't empty)?

Indeed! I missed that part. So we still need a get/put_online_cpus()
protection around all of this.

Just for curiosity sake. Wouldn't it be simpler and less error prone to
make the ARM_DBG_READ/WRITE macros use the exception table and handle that
in the undefined instruction handler to avoid this hook dance?

Thanks,

	tglx

Thread

[PATCH 15/20] ARM/hw_breakpoint: Convert to hotplug state machine Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2016-11-17 19:40 +0100
  Re: [PATCH 15/20] ARM/hw_breakpoint: Convert to hotplug state machine Will Deacon <will.deacon@arm.com> - 2016-11-18 13:10 +0100
    Re: [PATCH 15/20] ARM/hw_breakpoint: Convert to hotplug state  machine Thomas Gleixner <tglx@linutronix.de> - 2016-11-18 14:20 +0100
      Re: [PATCH 15/20] ARM/hw_breakpoint: Convert to hotplug state machine Will Deacon <will.deacon@arm.com> - 2016-11-18 14:40 +0100
        Re: [PATCH 15/20] ARM/hw_breakpoint: Convert to hotplug state machine Will Deacon <will.deacon@arm.com> - 2016-11-18 14:50 +0100
          Re: [PATCH 15/20] ARM/hw_breakpoint: Convert to hotplug state  machine Thomas Gleixner <tglx@linutronix.de> - 2016-11-18 15:10 +0100
            Re: [PATCH 15/20] ARM/hw_breakpoint: Convert to hotplug state machine Will Deacon <will.deacon@arm.com> - 2016-11-18 15:20 +0100
        Re: [PATCH 15/20] ARM/hw_breakpoint: Convert to hotplug state  machine Thomas Gleixner <tglx@linutronix.de> - 2016-11-18 14:50 +0100
  [tip:smp/hotplug] ARM/hw_breakpoint: Convert to hotplug state  machine tip-bot for Sebastian Andrzej Siewior <tipbot@zytor.com> - 2016-11-21 17:00 +0100
  [tip:smp/hotplug] ARM/hw_breakpoint: Convert to hotplug state  machine tip-bot for Sebastian Andrzej Siewior <tipbot@zytor.com> - 2016-11-22 23:50 +0100

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