Subject: Re: [patch net-next v2 4/7] switchdev: introduce possibility to defer obj_add/del

From: Nikolay Aleksandrov <[email-masked]>
Date: Mon, 12 Oct 2015 16:34:25 +0200

On 10/12/2015 03:15 PM, Jiri Pirko wrote:
> From: Jiri Pirko <[email-masked]>
> 
> 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 <[email-masked]>
> ---
>  include/net/switchdev.h   |   1 +
>  net/switchdev/switchdev.c | 137 +++++++++++++++++++++++++++++++++++++---------
>  2 files changed, 112 insertions(+), 26 deletions(-)
> 
[snip]
> +
> +struct switchdev_obj_work {
> +	struct work_struct work;
> +	struct net_device *dev;
> +	struct switchdev_obj obj;
> +	bool add; /* add of del */
s/of/or/ ? :-)

> +};
> +
> +static void switchdev_port_obj_work(struct work_struct *work)
> +{
> +	struct switchdev_obj_work *ow =
> +			container_of(work, struct switchdev_obj_work, work);
> +	bool rtnl_locked = rtnl_is_locked();
> +	int err;
> +
> +	if (!rtnl_locked)
> +		rtnl_lock();
> +	if (ow->add)
> +		err = switchdev_port_obj_add_now(ow->dev, &ow->obj);
> +	else
> +		err = switchdev_port_obj_del_now(ow->dev, &ow->obj);
> +	if (err && err != -EOPNOTSUPP)
> +		netdev_err(ow->dev, "failed (err=%d) to %s object (id=%d)\n",
> +			   err, ow->add ? "add" : "del", ow->obj.id);
> +	if (!rtnl_locked)
> +		rtnl_unlock();
> +
> +	dev_put(ow->dev);
> +	kfree(ow);
> +}
> +
> +static int switchdev_port_obj_work_schedule(struct net_device *dev,
> +					    const struct switchdev_obj *obj,
> +					    bool add)
> +{
> +	struct switchdev_obj_work *ow;
> +
> +	ow = kmalloc(sizeof(*ow), GFP_ATOMIC);
> +	if (!ow)
> +		return -ENOMEM;
> +
> +	INIT_WORK(&ow->work, switchdev_port_obj_work);
> +
This can be called without rtnl, what stops the device from disappearing
between the above and the hold below ?

> +	dev_hold(dev);
> +	ow->dev = dev;
> +	memcpy(&ow->obj, obj, sizeof(ow->obj));
> +	ow->add = add;
> +
> +	queue_work(switchdev_wq, &ow->work);
> +	return 0;
> +}
> +
[snip]