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Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace() methods

From "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Newsgroups linux.kernel
Subject Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace() methods
Date 2016-03-18 01:40 +0100
Message-ID <rdQCm-6sf-13@gated-at.bofh.it> (permalink)
References <rdLW2-35m-9@gated-at.bofh.it> <rdLW2-35m-11@gated-at.bofh.it> <rdLW2-35m-7@gated-at.bofh.it> <rdP3B-5d9-35@gated-at.bofh.it> <rdPmW-5Fn-19@gated-at.bofh.it>
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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

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Thread

Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace()  methods Peter Zijlstra <peterz@infradead.org> - 2016-03-17 20:40 +0100
  Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace()  methods Chris Metcalf <cmetcalf@mellanox.com> - 2016-03-17 23:40 +0100
    Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace()  methods Peter Zijlstra <peterz@infradead.org> - 2016-03-17 23:40 +0100
      Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace()  methods Peter Zijlstra <peterz@infradead.org> - 2016-03-18 00:20 +0100
  Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace()  methods "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-03-18 00:00 +0100
    Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace()  methods Peter Zijlstra <peterz@infradead.org> - 2016-03-18 00:10 +0100
    Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace()  methods Peter Zijlstra <peterz@infradead.org> - 2016-03-18 00:20 +0100
      Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace()  methods "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-03-18 01:40 +0100
    Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace()  methods Chris Metcalf <cmetcalf@mellanox.com> - 2016-03-18 01:20 +0100
      Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace()  methods "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-03-18 01:50 +0100
        Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace()  methods Daniel Thompson <daniel.thompson@linaro.org> - 2016-03-18 10:50 +0100
          Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace()  methods "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-03-19 01:00 +0100

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