linux-kernel - Re: [PATCH] prevent sparc64 from invoking irq handlers on offline CPUs

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Date:	Tue, 9 Sep 2008 07:54:53 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	David Miller <davem@...emloft.net>
Cc:	linux-kernel@...r.kernel.org, wli@...omorphy.com,
	sparclinux@...r.kernel.org, manfred@...orfullife.com,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] prevent sparc64 from invoking irq handlers on offline
	CPUs

On Mon, Sep 08, 2008 at 05:17:08PM -0700, David Miller wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> Date: Wed, 3 Sep 2008 08:42:17 -0700
> > o	Timer irqs.  Not sure what happens to add_timer() calls from
> > 	a CPU that is going offline.  The hope would be that they get
> > 	queued to some other CPU?
> 
> This case is interesting, and I'm no sure what happens here.

It turns out that there is a timer_cpu_modifier() that invokes
migrate_timers() upon CPU_DEAD or CPU_DEAD_FROZEN.  And migrate_timers()
looks like it does what its name says.  And I believe that CPU_DEAD
happens after sparc64's local_irq_enable() window, so we should be OK.

							Thanx, Paul
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