linux-kernel - Re: dst_ifdown breaks infiniband?

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Message-ID: <20070319121310.GE18497@mellanox.co.il>
Date:	Mon, 19 Mar 2007 14:13:10 +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>,
	David Miller <davem@...emloft.net>
Subject: Re: dst_ifdown breaks infiniband?

> Quoting Alexey Kuznetsov <kuznet@....inr.ac.ru>:
> Subject: Re: dst_ifdown breaks infiniband?
> 
> Hello!
> 
> > If a device driver sets neigh_destructor in neigh_params, this could
> > get called after the device has been unregistered and the driver module
> > removed.
> 
> It is the same problem: if dst->neighbour holds neighbour, it should
> not hold device. parms->dev is not supposed to be used after
> neigh_parms_release(). F.e. set parms->dev to NULL to catch bad references.

Yes. I fixed that - simply checking that neighbour->dev is a
loopback device is sufficient to detect the fact that
the device is being unregistered.

> Do you search for a way to find real inifiniband device in
> ipoib_neigh_destructor()?

No, not anymore.

> I guess you will not be able.

I agree it's not possible.

> The problem is logical: if destructor needs device, neighbour entry
> _somehow_ have to hold reference to the device (via neigh->dev, neigh->parms,
> whatever). Hence, if we hold neighbour entry, unregister cannot be completed.
> Therefore, destructor cannot refer to device. Q.E.D. :-)
> 
> Seems, releasing dst->neighbour is inevitable.

infiniband sets parm->neigh_destructor, and I search for a way to prevent
this destructor from being called after the module has been unloaded.
Ideas?

-- 
MST
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