linux-kernel - Re: Device hang when offlining a CPU due to IRQ misrouting

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Date:	Tue, 5 Jun 2007 10:36:47 -0700
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
Cc:	linux-kernel@...r.kernel.org, ebiederm@...ssion.com
Subject: Re: Device hang when offlining a CPU due to IRQ misrouting

On Tue, Jun 05, 2007 at 10:23:10AM -0700, Siddha, Suresh B wrote:

> Darrick, I see a kernel bug in this area(which is already filled with bugs,
> and I am looking into ways to fix them). Are you making sure that
> between step-1 and step-2, that interrupts actually started arriving at cpu1?
> 
> i.e., do step-1 and wait till the irq's start hitting at cpu1. At this point
> do step-2 and let us know if you still hit this bug?

Yes, the bug only happens after CPU1 begins to receive interrupts.

> > There exists a similar scenario.  Set the IRQ affinity to a bunch of
> > CPUs, watch /proc/interrupts to see which CPU is actually servicing the
> > interrupts, then offline that CPU.  The kernel does not reroute the IRQ
> > to any of the other CPUs and the device also hangs.
> 
> Is this a theory or did you observe this problem happening?

Nope, I've observed this situation too.

--D

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