Date: Thu, 17 Mar 2016 17:28:15 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>,
        Russell King <linux@arm.linux.org.uk>,
        Thomas Gleixner <tglx@linutronix.de>,
        Aaron Tomlin <atomlin@redhat.com>, Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@osdl.org>,
        Daniel Thompson <daniel.thompson@linaro.org>, x86@kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace()
 methods
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On Fri, Mar 18, 2016 at 12:11:28AM +0100, Peter Zijlstra wrote:
> On Thu, Mar 17, 2016 at 03:55:57PM -0700, Paul E. McKenney wrote:
> > The RCU stall-warn stack traces can be ugly, agreed.
> 
> Ugly isn't the problem, completely random bollocks that puts you on the
> wrong path was more the problem.
> 
> It uses a stack pointer saved at some random time in the past to start
> unwinding an active stack from. Completely and utter misery.

Yep, its accuracy does depend on what is going on, which was also my
experience with the NMI-based approach's reliablity.

Perhaps a boot-time parameter enabling the sysadm to pick the desired
flavor of poison?

							Thanx, Paul