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Date: Wed, 26 Feb 2003 10:47:23 -0800
From: Andrew Morton <akpm@digeo.com>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: davej@codemonkey.org.uk, schlicht@uni-mannheim.de, torvalds@transmeta.com,
       hugh@veritas.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH][2.5] fix preempt-issues with smp_call_function()
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Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
>
> On Wed, 2003-02-26 at 10:28, Andrew Morton wrote:
> > Dave Jones <davej@codemonkey.org.uk> wrote:
> > >
> > > btw, (unrelated) shouldn't smp_call_function be doing magick checks
> > > with cpu_online() ?
> > 
> > Looks OK?  It sprays the IPI out to all the other CPUs in cpu_online_map,
> > and waits for num_online_cpus()-1 CPUs to answer.
> 
> You cannot do that by counting without a lot of care. IPI messages do not have
> guaranteed "once only" semantics. On an error a resend can and has been observed
> to cause a reissue of an IPI on PII/PIII setups

If that resend results in delivery of an actual extra interrupt, the
resent-to CPU can start playing with stuff which used to be on the sender's
stack and the box goes splat.

Didn't sct have a fix for that?
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