linux-kernel - Re: [RFC v3 1/9] sysrq: Implement __handle_sysrq

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Message-ID: <20140425124530.52fd696c@gandalf.local.home>
Date:	Fri, 25 Apr 2014 12:45:30 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Daniel Thompson <daniel.thompson@...aro.org>
Cc:	kgdb-bugreport@...ts.sourceforge.net,
	Jason Wessel <jason.wessel@...driver.com>, patches@...aro.org,
	linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	John Stultz <john.stultz@...aro.org>,
	Anton Vorontsov <anton.vorontsov@...aro.org>,
	Colin Cross <ccross@...roid.com>, kernel-team@...roid.com
Subject: Re: [RFC v3 1/9] sysrq: Implement __handle_sysrq_nolock to avoid
 recursive locking in kdb

On Fri, 25 Apr 2014 17:29:22 +0100
Daniel Thompson <daniel.thompson@...aro.org> wrote:

> If kdb is triggered using SysRq-g then any use of the sr command results
> in the SysRq key table lock being recursively acquired, killing the debug
> session. That patch resolves the problem by introducing a _nolock
> alternative for __handle_sysrq.
> 
> Strictly speaking this approach risks racing on the key table when kdb is
> triggered by something other than SysRq-g however in that case any other
> CPU involved should release the spin lock before kgdb parks the slave
> CPUs.

Is that case documented somewhere in the code comments?

-- Steve
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