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

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Message-ID: <20070605184015.GF17143@linux-os.sc.intel.com>
Date:	Tue, 5 Jun 2007 11:40:15 -0700
From:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
To:	"Darrick J. Wong" <djwong@...ibm.com>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	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 11:33:01AM -0700, Darrick J. Wong wrote:
> On Tue, Jun 05, 2007 at 11:13:42AM -0700, Siddha, Suresh B wrote:
> > I see. Your system should have 4 or 8 logical cpu's right. So you must be
> > using logical flat mode, right?
> 
> I believe so.  The system has two Xeon 5150s with an Intel 5000 chipset
> of some sort.
> 
> > When this bug happens, what does /proc/irq/<irq-no>/smp_affinity show?
> 
> root@...3a188:~# cat /proc/irq/114/smp_affinity 
> 02

Ok. What this shows is that fixup_irqs() failed to move the irq properly.
Ideally we should see cpu_online_map here (i.e., 0xfd).

So most likely __assign_irq_vector() failed for some reason and I am
puzzled for the reason...

Does this problem happen only under certain stress or something simple, like

boot the kernel
echo 2 > /proc/irq/114/smp_affinity
wait for irq to hit the cpu1.
echo 0 > /sys/devices/system/cpu/cpu1/online

will immmd trigger this?

thanks,
suresh
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