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Date: Sat, 7 Feb 2009 13:24:32 +0100
From: Jarek Poplawski <jarkao2@gmail.com>
To: David Miller <davem@davemloft.net>
Cc: itvirta@iki.fi, linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: Soft lockup in sungem on Netra AC200 when switching interface
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David Miller wrote, On 02/07/2009 07:01 AM:

> From: Ilkka Virta <itvirta@iki.fi>
> Date: Fri, 6 Feb 2009 13:29:02 +0200
> 
>> Looking at gem_do_start() and gem_open(), it seems that the only thing
>> done while opening the device after the request_irq(), is a call to
>> napi_enable().
>>
>> I don't know what the ordering requirements are for the
>> initialization, but I boldly tried to move the napi_enable() call
>> inside gem_do_start() before the link state is checked and interrupts
>> subsequently enabled, and it seems to work for me. Doesn't even break
>> anything too obvious...
>>
>> Any ideas on how this really should be fixed?
> 
> Actually your fix looks good, I'll apply this :-)

Alas it could be not enough. It seems this problem is caused by not
serving interrupts if napi is disabled. This patch added napi_enable()
on one path, but e.g. here:

static int gem_close(struct net_device *dev)
{
        struct gem *gp = netdev_priv(dev);

        mutex_lock(&gp->pm_mutex);

        napi_disable(&gp->napi);

        gp->opened = 0;
        if (!gp->asleep)
                gem_do_stop(dev, 0);
...

similar storm can happen if an interrupt is triggered just after
napi_disable().

Jarek P.