netdev - Re: [PATCH net-next v4 2/2] vxlan: allow specifying multiple default destinations

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Message-ID: <CAF1J0HOKKZhjs+M++d0LwYBYSexD9Cx84t7MUmu6Gk39PDfXrw@mail.gmail.com>
Date:	Mon, 24 Jun 2013 08:57:55 +0300
From:	Mike Rapoport <mike.rapoport@...ellosystems.com>
To:	Stephen Hemminger <stephen@...workplumber.org>
Cc:	netdev@...r.kernel.org, David Stevens <dlstevens@...ibm.com>,
	Thomas Graf <tgraf@...g.ch>
Subject: Re: [PATCH net-next v4 2/2] vxlan: allow specifying multiple default destinations

On Mon, Jun 24, 2013 at 3:14 AM, Stephen Hemminger
<stephen@...workplumber.org> wrote:
> On Sun, 23 Jun 2013 19:22:23 +0300
> Mike Rapoport <mike.rapoport@...ellosystems.com> wrote:
>
>> A list of multiple default destinations can be used in environments that
>> disable multicast on the infrastructure level, e.g. public clouds.
>>
>> Signed-off-by: Mike Rapoport <mike.rapoport@...ellosystems.com>
>> ---
>>  drivers/net/vxlan.c          | 268 +++++++++++++++++++++++++++++++++++++++++--
>>  include/uapi/linux/if_link.h |  17 +++
>>  2 files changed, 276 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
>> index e5fb6568..f57a0d94 100644
>> --- a/drivers/net/vxlan.c
>> +++ b/drivers/net/vxlan.c
>> @@ -103,6 +103,7 @@ struct vxlan_rdst {
>>       u32                      remote_vni;
>>       u32                      remote_ifindex;
>>       struct list_head         list;
>> +     struct rcu_head          rcu;
>>  };
>
> The use of remotes_cnt here is not SMP safe.
> You are using remotes_cnt to size the buffer for dumping, but then the list
> of remotes might change during the dump.

The remotes_cnt is used only in netlink callbacks with rtnl_lock held
and it cannot be modified otherwise, so I don't see why it is not SMP
safe.

> There a a couple of alternatives here:
> 1. Put a hard limit on the number of remotes per MAC.
> 2. When there are multiple destnations, just dump multiple entries, like
>    multipath routing does.
>
> I prefer #2 because it also allows for a cleaner API on creation.
>



--
Sincerely yours,
Mike.
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