linux-kernel - Re: [PATCH] generic-ipi: fix deadlock in __smp_call_function

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Message-ID: <20100926125945.GA2597@osiris.boeblingen.de.ibm.com>
Date:	Sun, 26 Sep 2010 14:59:45 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Venkatesh Pallipadi <venki@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH] generic-ipi: fix deadlock in __smp_call_function_single

On Sun, Sep 26, 2010 at 10:42:33AM +0200, Ingo Molnar wrote:
> 
> * Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > Maybe.  Or maybe it papers over a scheduler bug by gratuitously adding 
> > additional code which no present callsites actually need.
> 
> Hm, indeed.
> 
> We now have the scheduler bug fixed upstream. Do we really need this 
> patch?

General consensus was that it is good if smp_call_function_single() and
__smp_call_function_single() would behave the same if remote cpu == current
cpu.

If you're not applying this patch then at least at a WARN_ON() which triggers
when remote cpu == current cpu. I don't want to debug something like this
again.
 
> > The patch didn't update the __smp_call_function_single() kerneldoc. 
> > Compare it with smp_call_function_single() and note the subtle 
> > difference between "a specific CPU" and the now incorrect "on another 
> > CPU".
> 
> In any case this feedback didnt get addressed AFAICS.

It did get addressed in an updated patch which is the one which you
applied: http://lkml.org/lkml/2010/9/10/245
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