netdev - Re: dst_ifdown breaks infiniband?

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Message-ID: <20070319120534.GA28187@ms2.inr.ac.ru>
Date:	Mon, 19 Mar 2007 15:05:34 +0300
From:	Alexey Kuznetsov <kuznet@....inr.ac.ru>
To:	"Michael S. Tsirkin" <mst@....mellanox.co.il>
Cc:	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?

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.

Do you search for a way to find real inifiniband device in
ipoib_neigh_destructor()? I guess you will not be able.
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.

Alexey
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