Subject: Re: [PATCH 0/3] Shared NMI backtracing support for ARM/x86
To: Russell King - ARM Linux <linux@arm.linux.org.uk>,
        linux-arm-kernel@lists.infradead.org, x86@kernel.org
References: <20150715203911.GF7557@n2100.arm.linux.org.uk>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@kernel.org>,
        linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>
From: Daniel Thompson <daniel.thompson@linaro.org>
Message-ID: <55A77F87.4050508@linaro.org>
Date: Thu, 16 Jul 2015 10:55:19 +0100
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On 15/07/15 21:39, Russell King - ARM Linux wrote:
> Back in September, I stumbled across a single CPU IRQs-off lockup of an
> ARM SMP system, and decided to hack something together based on a much
> older hacky implementation used with StrongARM CPUs from early 2000s.
>
> This resulted in a copy of the x86 NMI backtrace code into ARM as it was
> back then, and feedback indicated that it wasn't a good time to push
> such an effort forward, as printk() in NMI context is dodgy.
>
> Over time, the x86 code has had this problem addressed, and last week
> I updated the patch which I've been carrying in my tree to move the
> shared code out of arch/x86 into lib/ rather than duplicating it, and
> switch the ARM implementation to use it.
>
> Discussing this with Thomas Gliexner, he agreed to give it a test over
> last weekend, and he has reported to me this evening "no explosion so
> far".  Since then, I've made a change to add the NOKPROBE_SYMBOL() to
> the generic handler as per the x86 original code.
>
> I'm aware that there are other competing implementations out there -
> Daniel has one based on my patch from September time, but I don't think
> that goes far enough with code sharing.  I'm also partially aware of
> an implementation from Petr too.

No worries. I agree this approach is much cleaner with regards to code 
sharing.


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