Re: [RFC PATCH 00/11] printk: safe printing in NMI context

[Paul E. McKenney]

On Wed, Jun 18, 2014 at 04:41:09PM +0200, Jiri Kosina wrote:
> On Wed, 18 Jun 2014, Paul E. McKenney wrote:
> 
> > > - both RCU stall detector and 'echo l > sysrq-trigger' can (and we've 
> > >   seen it happening for real) cause a complete, undebuggable, silent hang 
> > >   of machine (deadlock in NMI context)
> > 
> > I could easily add an option to RCU to allow people to tell it not to
> > use NMIs to dump the stack.  Would that help?
> 
> Well, that would make unfortunately the information provided by RCU stall 
> detector rather useless ... workqueue-based stack dumping is very unlikely 
> to point its finger to the real offender, as it'd be coming way too late.

I would not use workqueues, but rather have the CPU detecting the
stall grovel through the other CPUs' stacks, which is what I do now for
architectures that don't support NMI-based stack dumps.  Would that be
a reasonable approach?

							Thanx, Paul

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