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Date:	Sun, 18 Mar 2007 22:24:44 +0200
From:	"Michael S. Tsirkin" <mst@....mellanox.co.il>
To:	Alexey Kuznetsov <kuznet@....inr.ac.ru>
Cc:	"Michael S. Tsirkin" <mst@....mellanox.co.il>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org, general@...ts.openfabrics.org,
	Roland Dreier <rolandd@...co.com>
Subject: Re: dst_ifdown breaks infiniband?

> Quoting Alexey Kuznetsov <kuznet@....inr.ac.ru>:
> Subject: Re: dst_ifdown breaks infiniband?
> 
> Hello!
> 
> > Hmm. Something I don't understand: does the code
> > in question not run on *each* device unregister?
> 
> It does.
> 
> 
> > Why do I only see this under stress?
> 
> You should have some referenced destination entries to trigger bad path.
> This should happen not only under stress.
> 
> F.e. just try to ssh to something via this device. And unregister it.
> Seems, the crash is inevitable. If you do not see crash, I will be puzzled.


I did this.
What happens is:

	neigh_setup is called
	dst_ifdown changes the neigh->dev to loopback device

But the funny thing is that this neighbour can thinkably hang
around indefinitely now, and if it does destructor won't be called
and there won't be a crash.

To trigger a crash, I did simply
	ifconfig lo down; ifconfig lo 127.0.0.1

and sure enough it crashes in drivers/infiniband/ulp/ipoib/ipoib_main.c.

-- 
MST
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