linux-kernel - Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu

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Date:	Thu, 17 Mar 2016 20:17:59 -0400
From:	Chris Metcalf <cmetcalf@...lanox.com>
To:	<paulmck@...ux.vnet.ibm.com>, Peter Zijlstra <peterz@...radead.org>
CC:	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Aaron Tomlin <atomlin@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Andrew Morton <akpm@...l.org>,
	Daniel Thompson <daniel.thompson@...aro.org>, <x86@...nel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace()
 methods

On 3/17/2016 6:55 PM, Paul E. McKenney wrote:
> The RCU stall-warn stack traces can be ugly, agreed.
>
> That said, RCU used to use NMI-based stack traces, but switched to the
> current scheme due to the NMIs having the unfortunate habit of locking
> things up, which IIRC often meant no stack traces at all.  If I recall
> correctly, one of the problems was self-deadlock in printk().

Steven Rostedt enabled the per_cpu printk func support in June 2014, and
the nmi_backtrace code uses it to just capture printk output to percpu
buffers, so I think it's going to be a lot more robust than earlier attempts.

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com