linux-kernel - Re: [PATCH 1/10] Add generic helpers for arch IPI function calls

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Message-ID: <20080502130922.GC15522@linux.vnet.ibm.com>
Date:	Fri, 2 May 2008 06:09:22 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Keith Owens <kaos@....com.au>
Cc:	Nick Piggin <npiggin@...e.de>, Jens Axboe <jens.axboe@...cle.com>,
	linux-kernel@...r.kernel.org, peterz@...radead.org,
	linux-arch@...r.kernel.org, jeremy@...p.org, mingo@...e.hu
Subject: Re: [PATCH 1/10] Add generic helpers for arch IPI function calls

On Fri, May 02, 2008 at 10:50:44PM +1000, Keith Owens wrote:
> "Paul E. McKenney" (on Fri, 2 May 2008 05:29:55 -0700) wrote:
> >OK -- for some reason, I was thinking that it was illegal to
> >invoke smp_call_function() with irqs disabled...
> >
> >Ah, I see it -- smp_call_function_mask() says:
> >
> > * You must not call this function with disabled interrupts or from a
> > * hardware interrupt handler or from a bottom half handler.
> >
> >So we have no problem with smp_call_function, then.
> >
> >OK, so smp_call_function() -can- be invoked with irqs disabled?
> >Hmmm...  I will give this some thought.
> 
> Doing any smp_call_function with interrupts disabled is a potential
> deadlock.  See http://lkml.org/lkml/2004/5/2/116.

OK, cool, thank you for the confirmation!

Therefore, when you call smp_call_function(), you may get calls from
other CPUs showing up, and therefore my polling approach does not
introduce any new strands of spaghetti.  ;-)

						Thanx, Paul
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