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Date:	Fri, 20 Jun 2014 01:03:28 +0200 (CEST)
From:	Jiri Kosina <>
To:	Steven Rostedt <>
	Linus Torvalds <>,
	Ingo Molnar <>,
	Andrew Morton <>,
	Michal Hocko <>, Jan Kara <>,
	Frederic Weisbecker <>,
	Dave Anderson <>,
	Petr Mladek <>
Subject: Re: [RFC][PATCH 0/3] x86/nmi: Print all cpu stacks from NMI safely

On Thu, 19 Jun 2014, Steven Rostedt wrote:

> > The idea basically is to *switch* what arch_trigger_all_cpu_backtrace() 
> > and arch_trigger_all_cpu_backtrace_handler() are doing; i.e. use the NMI 
> > as a way to stop all the CPUs (one by one), and let the CPU that is 
> > sending the NMIs around to actually walk and dump the stacks of the CPUs 
> > receiving the NMI IPI.
> And this is cleaner? Stopping a CPU via NMI and then what happens if
> something else goes wrong and that CPU never starts back up? This
> sounds like something that can cause more problems than it was
> reporting on.

It's going to get NMI in exactly the same situations it does with the 
current arch_trigger_all_cpu_backtrace(), the only difference being that 
it doesn't try to invoke printk() from inside NMI. The IPI-NMI is used 
solely as a point of synchronization for the stack dumping.

> Then you also need to print out the data while the NMIs still spin.

Exactly, that's actually the whole point.


Jiri Kosina
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