linux-kernel - Re: [PATCH] prevent powerpc from invoking irq handlers on offline CPUs

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Message-Id: <1220238880.13010.4.camel@pasglop>
Date:	Mon, 01 Sep 2008 13:14:40 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org, paulus@...ba.org,
	jwboyer@...ux.vnet.ibm.com, tnt@...tNt.com,
	grant.likely@...retlab.ca, linuxppc-dev@...abs.org,
	manfred@...orfullife.com, akpm@...ux-foundation.org
Subject: Re: [PATCH] prevent powerpc from invoking irq handlers on offline
	CPUs

On Sun, 2008-08-31 at 19:06 -0700, Paul E. McKenney wrote:
> On Mon, Sep 01, 2008 at 10:34:44AM +1000, Benjamin Herrenschmidt wrote:
> > On Sun, 2008-08-31 at 10:31 -0700, Paul E. McKenney wrote:
> > > Make powerpc refrain from clearing a given to-be-offlined CPU's bit in the
> > > cpu_online_mask until it has processed pending irqs.  This change
> > > prevents other CPUs from being blindsided by an apparently offline CPU
> > > nevertheless changing globally visible state.
> > > 
> > > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > > ---
> > 
> > Sounds reasonable... the only possible worry here is if somebody tries
> > an IPI ... The IPI code will and the target CPU mask with the online
> > map, so it may try to send to the to-be-offlined CPU and timeout, no ?
> 
> OK.  Do we need separate IPI and online masks?

Shouldn't we already have routed all interrupts to other CPUs anyway ?

IE. The affinity of all interrupts should have been updated. So the
only thing we're going to get here are possibly IPIs and decrementer, 
I don't see it being a big deal making sure we test we are online when
receiving it.

Ben.


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