netdev - Re: Fw: oops during unregister_netdevice interface enslaved to bond

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Date:	Tue, 10 May 2011 15:14:38 +0200
From:	Frank Blaschka <blaschka@...ux.vnet.ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, ELELUECK@...ibm.com
Subject: Re: Fw: oops during unregister_netdevice interface enslaved to
	bond - regression

On Tue, May 10, 2011 at 10:54:32AM +0200, Eric Dumazet wrote:
> Le mardi 10 mai 2011 à 10:17 +0200, Einar EL Lueck a écrit :
> > Hi Dave,
> > 
> > Einar EL Lueck/Germany/IBM wrote on 04/29/2011 04:45:45 PM:
> > 
> > > From:
> > >
> > > Einar EL Lueck/Germany/IBM
> > >
> > > To:
> > >
> > > opurdila@...acom.com, netdev@...r.kernel.org, linux-
> > > s390@...r.kernel.org, davem@...emloft.net
> > >
> > > Cc:
> > >
> > > Frank Blaschka/Germany/IBM@...DE
> > >
> > > Date:
> > >
> > > 04/29/2011 04:45 PM
> > >
> > > Subject:
> > >
> > > Re: oops during unregister_netdevice interface enslaved to bond -
> > regression
> > >
> > > Hi Octavian,
> > >
> > > On 04/15/2011 10:53 AM, Frank Blaschka wrote:
> > > > Hi Octavian,
> > > >
> > > > your commit 443457242beb6716b43db4d62fe148eab5515505 introduced
> > > this regression.
> > > > I have reviewed the net device unregister code but did not
> > > understand it very well.
> > > > I have seen the problem only in combination with bonding. Can you
> > > give me some help
> > > > how to go on with this problem. I can reproduced it very easy on
> > asingle CPU
> > > > machine.
> > > >
> > >
> > > In this case rollback_registered_many iterates over the list of devs
> > > that initially has just one device in it. In a loop it calls
> > > call_netdevice_notifiers(NETDEV_UNREGISTER, dev) which triggers the
> > > bonding driver to call dev_close_many for the same device. That call
> > > to dev_close_many leads to the addition of the same device to the
> > > list over which rollback_registered_many is iterating. Consequently,
> > > netdev_unregister_kobject(dev) is called twice for the same device.
> > > Frank captured the result in his mail.
> > >
> > 
> > Calls to the *_many functions introduced by Octavian may never interleave
> > because
> > the traversed lists modify each other. This was the root cause for the
> > symptom that Frank discovered. Octavian is not a valid mail recipient
> > anymore and did not react from any new mail address. I suggest to revert
> > the commit.
> > 
> 
> Hello Einar
> 
> I am currently working on this stuff [adding even more batching and
> probably bugs as well ], so instead of revert I'll try to find a way to
> fix this.
>
great Thx!
 
> If you already have a script to reproduce the bug on virtual devices on
> x86 (not on s390 machines I dont have ;) ), I'll appreciate having a
> copy of it.a

I just checked todays net-next tree, problem is still there.
I don't have an x86 box, but I was able to reproduce the problem
with the dummy device (on s/390)

# modprobe bonding
# modprobe dummy
# ifconfig bond0 up
# ifenslave bond0 dummy0
# rmmod dummy

oops looks very much the same as unsing a real device. Hope this helps ...
> 
> Thanks for the reminder.
> 
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