linux-kernel - Re: [PATCH RFC v1 1/3] ARM: Add irq disabled version of soft

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Date:	Tue, 25 Feb 2014 11:27:52 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Russ Dill <Russ.Dill@...com>
cc:	Sebastian Capella <sebastian.capella@...aro.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linaro-kernel@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Will Deacon <will.deacon@....com>, Robin Holt <holt@....com>
Subject: Re: [PATCH RFC v1 1/3] ARM: Add irq disabled version of
 soft_restart.

On Mon, 24 Feb 2014, Russ Dill wrote:
> On 02/24/2014 03:13 PM, Sebastian Capella wrote:
> > Quoting Russell King - ARM Linux (2014-02-22 02:26:17)
> >> On Tue, Feb 18, 2014 at 05:52:07PM -0800, Sebastian Capella wrote:
> >>> From: Russ Dill <Russ.Dill@...com>
> >>>
> >>> This adds the ability to run soft_restart with local_irq/fiq_disable
> >>> already called. This is helpful for the hibernation code paths.
> >>
> >> I'd rather keep this simple.  There's no problem with calling soft_restart
> >> with interrupts already disabled.  local_irq_disable()/local_fiq_disable()
> >> there should be harmless.
> > 
> > Hi Russell,
> > 
> > I'm observing a data abort loop when I replace this call:
> > 
> > In the local_irq_disable, it ends up calling trace_hardirqs_off
> > (CONFIG_TRACE_IRQFLAGS_SUPPORT is enabled), which calls
> > trace_hardirqs_off_caller which checks lockdep_recursion in the
> > current task, but we've switched to a temporary stack with the
> > call_with_stack, and get_current is returning NULL.  This
> > triggers a data abort, which calls trace_hardirqs_off
> > again and so on.
> > 
> > Do you have any suggestions here?
> > 
> > Thanks,
> > 
> > Sebastian
> > 
> 
> So the alternative is to have a version of the call that calls a special
> no trace version of local_irq_disable()/local_fiq_disable(). Which would
> be preferable? Having a noirq version of soft_restart seems much simpler
> to me.

If you want escape the tracer and in that case you really want it
being on a different stack, use raw_local_irq_* which are not traced.

Thanks,

	tglx


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