netdev - Re: [patch net-next v3 11/12] mlxsw: spectrum_router: Request a dump of FIB tables during init

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Date:   Thu, 1 Dec 2016 22:09:54 +0100
From:   Hannes Frederic Sowa <hannes@...essinduktion.org>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org,
        davem@...emloft.net, idosch@...lanox.com, eladr@...lanox.com,
        yotamg@...lanox.com, nogahf@...lanox.com, arkadis@...lanox.com,
        ogerlitz@...lanox.com, roopa@...ulusnetworks.com,
        dsa@...ulusnetworks.com, nikolay@...ulusnetworks.com,
        andy@...yhouse.net, vivien.didelot@...oirfairelinux.com,
        andrew@...n.ch, f.fainelli@...il.com, alexander.h.duyck@...el.com,
        kaber@...sh.net
Subject: Re: [patch net-next v3 11/12] mlxsw: spectrum_router: Request a dump
 of FIB tables during init

On 30.11.2016 17:32, Ido Schimmel wrote:
> Hi Hannes,
> 
> On Wed, Nov 30, 2016 at 04:37:48PM +0100, Hannes Frederic Sowa wrote:
>> On 30.11.2016 11:09, Jiri Pirko wrote:
>>> From: Ido Schimmel <idosch@...lanox.com>
>>>
>>> Make sure the device has a complete view of the FIB tables by invoking
>>> their dump during module init.
>>>
>>> Signed-off-by: Ido Schimmel <idosch@...lanox.com>
>>> Signed-off-by: Jiri Pirko <jiri@...lanox.com>
>>> ---
>>>  .../net/ethernet/mellanox/mlxsw/spectrum_router.c  | 23 ++++++++++++++++++++++
>>>  1 file changed, 23 insertions(+)
>>>
>>> diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
>>> index 14bed1d..d176047 100644
>>> --- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
>>> +++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
>>> @@ -2027,8 +2027,23 @@ static int mlxsw_sp_router_fib_event(struct notifier_block *nb,
>>>  	return NOTIFY_DONE;
>>>  }
>>>  
>>> +static void mlxsw_sp_router_fib_dump_flush(struct notifier_block *nb)
>>> +{
>>> +	struct mlxsw_sp *mlxsw_sp = container_of(nb, struct mlxsw_sp, fib_nb);
>>> +
>>> +	/* Flush pending FIB notifications and then flush the device's
>>> +	 * table before requesting another dump. Do that with RTNL held,
>>> +	 * as FIB notification block is already registered.
>>> +	 */
>>> +	mlxsw_core_flush_owq();
>>> +	rtnl_lock();
>>> +	mlxsw_sp_router_fib_flush(mlxsw_sp);
>>> +	rtnl_unlock();
>>> +}
>>> +
>>>  int mlxsw_sp_router_init(struct mlxsw_sp *mlxsw_sp)
>>>  {
>>> +	fib_dump_cb_t *cb = mlxsw_sp_router_fib_dump_flush;
>>>  	int err;
>>>  
>>>  	INIT_LIST_HEAD(&mlxsw_sp->router.nexthop_neighs_list);
>>> @@ -2048,8 +2063,16 @@ int mlxsw_sp_router_init(struct mlxsw_sp *mlxsw_sp)
>>>  
>>>  	mlxsw_sp->fib_nb.notifier_call = mlxsw_sp_router_fib_event;
>>>  	register_fib_notifier(&mlxsw_sp->fib_nb);
>>
>> Sorry to pick in here again:
>>
>> There is a race here. You need to protect the registration of the fib
>> notifier as well by the sequence counter. Updates here are not ordered
>> in relation to this code below.
> 
> You mean updates that can be received after you registered the notifier
> and until the dump started? I'm aware of that and that's OK. This
> listener should be able to handle duplicates.

I am not concerned about duplicates, but about ordering deletes and
getting an add from the RCU code you will add the node to hw while it is
deleted in the software path. You probably will ignore the delete
because nothing is installed in hw and later add the node which was
actually deleted but just reordered which happend on another CPU, no?

> I've a follow up patchset that introduces a new event in switchdev
> notification chain called SWITCHDEV_SYNC, which is sent when port
> netdevs are enslaved / released  from a master device (points in time
> where kernel<->device can get out of sync). It will invoke
> re-propagation of configuration from different parts of the stack
> (e.g. bridge driver, 8021q driver, fib/neigh code), which can result
> in duplicates.

Okay, understood. I wonder how we can protect against accidentally abort
calls actually. E.g. if I start to inject routes into my routing domain
how can I make sure the box doesn't die after I try to insert enough
routes. Do we need to touch quagga etc?

Thanks,
Hannes