netdev - Re: [patch net-next v5 5/8] switchdev: introduce possibility to defer obj

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Date:	Mon, 19 Oct 2015 00:55:59 -0700
From:	Scott Feldman <sfeldma@...il.com>
To:	Jiri Pirko <jiri@...nulli.us>
Cc:	Netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Ido Schimmel <idosch@...lanox.com>,
	Elad Raz <eladr@...lanox.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
	"andrew@...n.ch" <andrew@...n.ch>,
	john fastabend <john.fastabend@...il.com>,
	David Laight <David.Laight@...lab.com>,
	"stephen@...workplumber.org" <stephen@...workplumber.org>
Subject: Re: [patch net-next v5 5/8] switchdev: introduce possibility to defer obj_add/del

On Wed, Oct 14, 2015 at 10:40 AM, Jiri Pirko <jiri@...nulli.us> wrote:
> From: Jiri Pirko <jiri@...lanox.com>
>
> Similar to the attr usecase, the caller knows if he is holding RTNL and is
> in atomic section. So let the called to decide the correct call variant.
>
> This allows drivers to sleep inside their ops and wait for hw to get the
> operation status. Then the status is propagated into switchdev core.
> This avoids silent errors in drivers.
>
> Signed-off-by: Jiri Pirko <jiri@...lanox.com>
> ---
>  include/net/switchdev.h   |   1 +
>  net/switchdev/switchdev.c | 100 ++++++++++++++++++++++++++++++++++++----------
>  2 files changed, 81 insertions(+), 20 deletions(-)
>
> diff --git a/include/net/switchdev.h b/include/net/switchdev.h
> index f8672d7..bc865e2 100644
> --- a/include/net/switchdev.h
> +++ b/include/net/switchdev.h
> @@ -69,6 +69,7 @@ enum switchdev_obj_id {
>
>  struct switchdev_obj {
>         enum switchdev_obj_id id;
> +       u32 flags;
>  };
>
>  /* SWITCHDEV_OBJ_ID_PORT_VLAN */
> diff --git a/net/switchdev/switchdev.c b/net/switchdev/switchdev.c
> index 5963d7a..eac68c4 100644
> --- a/net/switchdev/switchdev.c
> +++ b/net/switchdev/switchdev.c
> @@ -362,21 +362,8 @@ static int __switchdev_port_obj_add(struct net_device *dev,
>         return err;
>  }
>
> -/**
> - *     switchdev_port_obj_add - Add port object
> - *
> - *     @dev: port device
> - *     @id: object ID
> - *     @obj: object to add
> - *
> - *     Use a 2-phase prepare-commit transaction model to ensure
> - *     system is not left in a partially updated state due to
> - *     failure from driver/device.
> - *
> - *     rtnl_lock must be held.
> - */
> -int switchdev_port_obj_add(struct net_device *dev,
> -                          const struct switchdev_obj *obj)
> +static int switchdev_port_obj_add_now(struct net_device *dev,
> +                                     const struct switchdev_obj *obj)
>  {
>         struct switchdev_trans trans;
>         int err;
> @@ -418,18 +405,53 @@ int switchdev_port_obj_add(struct net_device *dev,
>
>         return err;
>  }
> -EXPORT_SYMBOL_GPL(switchdev_port_obj_add);
> +
> +static void switchdev_port_obj_add_deferred(struct net_device *dev,
> +                                           const void *data)
> +{
> +       const struct switchdev_obj *obj = data;
> +       int err;
> +
> +       err = switchdev_port_obj_add_now(dev, obj);
> +       if (err && err != -EOPNOTSUPP)
> +               netdev_err(dev, "failed (err=%d) to add object (id=%d)\n",
> +                          err, obj->id);
> +}
> +
> +static int switchdev_port_obj_add_defer(struct net_device *dev,
> +                                       const struct switchdev_obj *obj)
> +{
> +       return switchdev_deferred_enqueue(dev, obj, sizeof(*obj),
> +                                         switchdev_port_obj_add_deferred);
> +}

Hi Jiri,

I think there is a problem here with this patch.  When we defer adding
an obj, we're only copying the inner struct switchdev_obj.  The rest
of the containing obj is lost.  So when
switchdev_port_obj_add_deferred() runs, we're up casting to garbage.
So if this FDB obj was deferred, the addr, vid, and ndm_state members
would be garbage:

struct switchdev_obj_port_fdb {
        struct switchdev_obj obj;
        unsigned char addr[ETH_ALEN];
        u16 vid;
        u16 ndm_state;
};
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