linux-kernel - Re: [PATCH 08/14] tty/serial/kgdboc: Add and wire up clear

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Message-ID: <20120910201918.1e3c8fd0@pyramind.ukuu.org.uk>
Date:	Mon, 10 Sep 2012 20:19:18 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Anton Vorontsov <anton.vorontsov@...aro.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Russell King <linux@....linux.org.uk>,
	Jason Wessel <jason.wessel@...driver.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alan Cox <alan@...ux.intel.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Colin Cross <ccross@...roid.com>,
	Brian Swetland <swetland@...gle.com>,
	John Stultz <john.stultz@...aro.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	kernel-team@...roid.com, kgdb-bugreport@...ts.sourceforge.net,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH 08/14] tty/serial/kgdboc: Add and wire up clear_irqs
 callback

On Mon, 10 Sep 2012 10:57:04 -0700
Anton Vorontsov <anton.vorontsov@...aro.org> wrote:

> On Mon, Sep 10, 2012 at 12:16:24PM +0100, Alan Cox wrote:
> > > serial port, the CPU receives NMI exception, and we fall into KDB
> > > shell.  So, it is our "debug console", and it is able to interrupt
> > > (and thus debug) even IRQ handlers themselves.
> > 
> > You seem to have an assumption of single core here. What happens if
> > the NMI hits CPU #0 and the serial IRQ hits CPU #1 simultaneously ?
> 
> If you can't redirect all serial IRQs to NMI context, e.g. sometimes you get
> NMIs, sometimes IRQs, then your NMI handling is not deterministic, and surely
> this is not supported.

This seems like arch specific magic leaking into the tty code. Surely
this should be buried in the depths of the platform IRQ code ?

Alan
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