linux-kernel - Re: [PATCH 4.0-rc1 v17 4/6] printk: Simple implementation for NMI backtracing

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Message-ID: <1425486786.2769.25.camel@linaro.org>
Date:	Wed, 04 Mar 2015 16:33:06 +0000
From:	Daniel Thompson <daniel.thompson@...aro.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Joe Perches <joe@...ches.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Russell King <linux@....linux.org.uk>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Marc Zyngier <marc.zyngier@....com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	John Stultz <john.stultz@...aro.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	patches@...aro.org, linaro-kernel@...ts.linaro.org,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Dirk Behme <dirk.behme@...bosch.com>,
	Daniel Drake <drake@...lessm.com>,
	Dmitry Pervushin <dpervushin@...il.com>,
	Tim Sander <tim@...eglstein.org>
Subject: Re: [PATCH 4.0-rc1 v17 4/6] printk: Simple implementation for NMI
 backtracing

On Wed, 2015-03-04 at 11:20 -0500, Steven Rostedt wrote:
> On Wed, 04 Mar 2015 08:13:21 -0800
> Joe Perches <joe@...ches.com> wrote:
> 
> > On Wed, 2015-03-04 at 10:12 +0000, Daniel Thompson wrote:
> > > Currently there is a quite a pile of code sitting in
> > > arch/x86/kernel/apic/hw_nmi.c to support safe all-cpu backtracing from NMI.
> > > The code is inaccessible to backtrace implementations for other
> > > architectures, which is a shame because they would probably like to be
> > > safe too.
> > > 
> > > Copy this code into printk. We'll port the x86 NMI backtrace to it in a
> > > later patch.
> > 
> > I think this would be better as a separate file
> > rather than increasing the bulk of printk.c
> > 
> 
> I agree, as printk already has its own directory. Perhaps a
> "nmi_backtrace.c"?

I agree on moving the code. However, after Thomas' review I made sure
all the external symbols were prefixed printk_nmi and, as a result of
the same review I started using CONFIG_PRINTK_NMI to enable/disable the
feature). For that reason I'm much more inclined to name it
"printk_nmi.c". Any objections?

I know it is a somewhat generic name but I'll move the comment text that
commences "This is not a generic printk() implementation and must be
used with great care. In particular..." to the top of the file to make
clear the limitations of this code.


Daniel.

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