netdev - Re: [PATCH] ipv6: Fix "waiting for %s to become free" hang

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Date:	Fri, 4 Dec 2009 17:45:47 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH] ipv6: Fix "waiting for %s to become free" hang

> Eric Dumazet <eric.dumazet@...il.com>
>
> Re: [PATCH] ipv6: Fix "waiting for %s to become free" hang
>
> Krishna Kumar a écrit :
> > From: Krishna Kumar <krkumar2@...ibm.com>
> >
> > (From code-walkthrough, and untested)
> >
> > Fix "waiting for %s to become free" hang. dev has an
> > extra hold (by ip6mr_reg_vif) which was not dropped
> > before calling unregister_netdevice.
> >
> > Signed-off-by: Krishna Kumar <krkumar2@...ibm.com>
> > ---
> >  net/ipv6/ip6mr.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff -ruNp org/net/ipv6/ip6mr.c new/net/ipv6/ip6mr.c
> > --- org/net/ipv6/ip6mr.c   2009-12-04 16:08:07.000000000 +0530
> > +++ new/net/ipv6/ip6mr.c   2009-12-04 16:09:56.000000000 +0530
> > @@ -648,8 +648,8 @@ static int mif6_add(struct net *net, str
> >           return -ENOBUFS;
> >        err = dev_set_allmulti(dev, 1);
> >        if (err) {
> > -         unregister_netdevice(dev);
> >           dev_put(dev);
> > +         unregister_netdevice(dev);
> >           return err;
> >        }
> >        break;
>
> This changes nothing, since we hold rtnl at this point.
>
> unregister_netdevice() only queues the device (net_set_todo()) in a list.
>
> And we process this list later, when renl_unlock() is finally called.

Yes, you are right. I sent the patch on my memory of unregister_netdev,
which gets
the rtnl and drops it, and that would have caused this problem. Please drop
the patch.

thanks,

- KK

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