linux-kernel - Re: [tip:core/debug] debug lockups: Improve lockup detection

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Date:	Mon, 3 Aug 2009 09:59:43 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	paulmck@...ux.vnet.ibm.com, mingo@...hat.com, hpa@...or.com,
	linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl,
	torvalds@...ux-foundation.org, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:core/debug] debug lockups: Improve lockup detection


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Sun, 2 Aug 2009 22:41:50 +0200 Ingo Molnar <mingo@...e.hu> wrote:
> 
> > 
> > * Andrew Morton <akpm@...ux-foundation.org> wrote:
> > 
> > > On Sun, 2 Aug 2009 21:26:57 +0200 Ingo Molnar <mingo@...e.hu> wrote:
> > > 
> > > > > I think this just broke all non-x86 non-sparc SMP architectures.
> > > > 
> > > > Yeah - it 'broke' them in the sense of them not having a working 
> > > > trigger_all_cpu_backtrace() implementation to begin with.
> > > 
> > > c'mon.  It broke them in the sense that sysrq-l went from "works" 
> > > to "doesn't work".
> > 
> > You are right (i broke it with my patch) but the thing is, 
> > sysrq-l almost useless currently: it uses schedule_work() which 
> > assumes a mostly working system with full irqs and scheduling 
> > working fine. Now, i dont need sysrq-l on mostly working 
> > systems.
> > 
> > So the 'breakage' is of something that was largely useless: and 
> > now you put the onus of implementing it for _all_ architectures 
> > (which i dont use) on me?
> 
> I never said that.
>
> It's appropriate that those architectures be left with their 
> existing level of functionality/usefulness, as you're already 
> discussing.

Ok, agreed.

> > > It's better to break the build or to emit warnings than to 
> > > silently and secretly break their stuff.
> > 
> > But that warning will bounce the ball back to me, wont it? My 
> > patch will be blamed for 'breaking' those architectures, right?
> 
> It's a very crude and somewhat rude way of communicating 
> information to other architecture maintainers.
>
> A better way would be to send them an email explaining the problem 
> and outlining some solutions, no?

I've restored the generic fallback code so there should be no change 
in functionality. I'll test it and push it out - you can check that 
patch via the commit notification email.

Thanks,

	Ingo
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