netdev - Re: [PATCH net/for-next V1 1/1] IB/ipoib: break linkage to neighbouring system

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Message-ID: <CAJZOPZ+kRcBjJgB_HaMqeuB5E-SLSqskgoaLZ_hvVx4KffHgpA@mail.gmail.com>
Date:	Fri, 20 Jul 2012 18:49:16 +0300
From:	Or Gerlitz <or.gerlitz@...il.com>
To:	roland@...nel.org, davem@...emloft.net
Cc:	linux-rdma@...r.kernel.org, erezsh@...lanox.com,
	Shlomo Pongratz <shlomop@...lanox.com>,
	Or Gerlitz <ogerlitz@...lanox.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net/for-next V1 1/1] IB/ipoib: break linkage to
 neighbouring system

On Thu, Jul 19, 2012 at 4:18 PM, Or Gerlitz <ogerlitz@...lanox.com> wrote:
> From: Shlomo Pongratz <shlomop@...lanox.com>
>
> Dave Miller <davem@...emloft.net> provided a detailed description of why the
> way IPoIB is using neighbours for its own ipoib_neigh struct is buggy:
[...]

> This patch aims to solve the race conditions found in the IPoIB driver.
>
> The patch breaks the connection between the core networking neighbour structure
> and the ipoib_neigh structure. Except for avoiding the race, it allows to in
> under a setup where SKBs carrying IP packets that don't have any associated
> neighbour are transmitted through IPoIB.
>
> We add an ipoib_neigh hash table with 1024 buckets. The hash table key is the destin
> hardware address. Thus the ipoib_neigh is fetched from the hash table and not
> dereferenced from the stashed location at the neighbour structure. The hash table uses
> both RCU and reference count mechanisms to guarantee that no ipoib_neigh instance is
> ever deleted while in use.
>
> Fetching the ipoib_neigh structure instance from the hash also makes the special
> code in ipoib_start_xmit that handles remote and local bonding failover redundant.
>
> Aged ipoib_neigh instances are deleted by a garbage collection task that runs every
> 30 seconds and deletes every ipoib_neigh instance that was idle for at least 60
> seconds. The deletion is safe since the ipoib_neigh instances are protected
> using RCU and reference count mechanisms.

Hi Dave, Roland, Eric

So how does this look? in the right direction? anything that need to be fixed?

Or.
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