netdev - Re: BUG: soft lockup detected on CPU#0! (2.6.18.2 plus hacks)

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Message-ID: <20070104082930.GB7006@gondor.apana.org.au>
Date:	Thu, 4 Jan 2007 19:29:30 +1100
From:	Herbert Xu <herbert.xu@...hat.com>
To:	Jarek Poplawski <jarkao2@...pl>
Cc:	David Stevens <dlstevens@...ibm.com>, greearb@...delatech.com,
	netdev@...r.kernel.org
Subject: Re: BUG: soft lockup detected on CPU#0!  (2.6.18.2 plus hacks)

On Thu, Jan 04, 2007 at 09:03:51AM +0100, Jarek Poplawski wrote:
> 
> I doubt this is the right solution. It certainly
> could fix this particular situation but my main
> point was packets shouldn't get into kernel
> receive queues with skb->dev not IFF_UP.

I think you misunderstood.  The device certainly is IFF_UP.  What
happens is that the multicast spin locks are set up too late:

        /* Account for reference dev->ip_ptr */
        in_dev_hold(in_dev);
        rcu_assign_pointer(dev->ip_ptr, in_dev);

As soon as we set ip_ptr incoming packets can cause the multicast
locks to be taken.

#ifdef CONFIG_SYSCTL
        devinet_sysctl_register(in_dev, &in_dev->cnf);
#endif

In fact the back trace shows that we get a packet during the
sysctl registration.

        ip_mc_init_dev(in_dev);

However, the spin locks are not setup until this point.  This is
exactly what David's patch fixes.

        if (dev->flags & IFF_UP)
                ip_mc_up(in_dev);

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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