netdev - Re: [PATCH net-next] rocker: move netevent neigh update to processes context

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Message-Id: <20150521.232945.93773536631316420.davem@davemloft.net>
Date:	Thu, 21 May 2015 23:29:45 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	sfeldma@...il.com
Cc:	netdev@...r.kernel.org, jiri@...nulli.us,
	simon.horman@...ronome.com, makita.toshiaki@....ntt.co.jp
Subject: Re: [PATCH net-next] rocker: move netevent neigh update to
 processes context

From: sfeldma@...il.com
Date: Wed, 20 May 2015 22:05:07 -0700

> From: Scott Feldman <sfeldma@...il.com>
> 
> In review of Simon's patchset "rocker: transaction fixes". it was noted
> that rocker->neigh_tbl_next_index was unprotected in the call path below
> and could race with other contexts calling rocker_port_ipv4_neigh():
> 
> 	arp_process()
> 	neigh_update()
> 	rocker_neigh_update()
> 	rocker_port_ipv4_neigh()
> 
> To fix, move the neigh_update() event processing to process contexts and
> hold rtnl_lock to call rocker_port_ipv4_neigh().  This will protect
> rocker->neigh_tbl_next_index accesses and is more consistent with the rest
> of the driver code where non-I/O processing is done under process context
> with rtnl_lock held.
> 
> Signed-off-by: Scott Feldman <sfeldma@...il.com>

Are you sure that the workqueue mechanism all by itself will ensure
that operations queued up will be processed in-order?

I do not know of any such explicit guarantee.

Therefore I think you will need a per-device workqueue with a list,
or something like that.

I could be wrong.
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