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Date:	Mon, 19 Mar 2007 07:15:20 +0200
From:	"Michael S. Tsirkin" <mst@....mellanox.co.il>
To:	"Michael S. Tsirkin" <mst@....mellanox.co.il>
Cc:	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	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 Michael S. Tsirkin <mst@....mellanox.co.il>:
> Subject: Re: dst_ifdown breaks infiniband?
> 
> > Quoting Michael S. Tsirkin <mst@....mellanox.co.il>:
> > Subject: Re: dst_ifdown breaks infiniband?
> > 
> > > Quoting Michael S. Tsirkin <mst@....mellanox.co.il>:
> > > Subject: Re: dst_ifdown breaks infiniband?
> > > 
> > > Quoting Alexey Kuznetsov <kuznet@....inr.ac.ru>:
> > > Subject: Re: dst_ifdown breaks infiniband?
> > > > > Can dst->neighbour be changed to point to NULL instead, and the neighbour
> > > > > released?
> > > > 
> > > > It should be cleared and we should be sure it will not be destroyed
> > > > before quiescent state.
> > > > 
> > > > Seems, this is the only correct solution, but to do this we have
> > > > to audit all the places where dst->neighbour is dereferenced for
> > > > RCU safety.
> > > > 
> > > > Actually, it is very good you caught this eventually, the bug was
> > > > so _disgusting_ that it was "forgotten" all the time, waiting for
> > > > someone who will point out that the king is naked. :-)
> > > 
> > > Actually that might not be too bad:
> > > $grep -rIi 'dst->neighbour' net/ | wc -l
> > > 36
> > > 
> > > I'll try to do it.
> > 
> > Here's the list. Looks OK to me. What do you think?
> > 
> 
> So Alexey, how does the following (lightly tested) patch look?
> Is this what you had in mind?
> 
> -----------------------------
> 
> Fix dst_ifdown for infiniband.
> 
> Changing dst->neighbour->dev is unsafe because neigh->parms callbacks
> are set up for specific device.
> We should drop the dst->neighbour reference instead.
> 
> Signed-off-by: Michael S. Tsirkin <mst@....mellanox.co.il>

Ugh, looked again and this looks obviously broken.
Note to self - stop writing code at 23:00.

-- 
MST
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