netdev - Re: [PATCH net-next v2 12/12] net-sysfs: move the xps cpus/rxqs retrieval in a common function

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Date:   Mon, 8 Feb 2021 14:45:32 -0800
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Antoine Tenart <atenart@...nel.org>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2 12/12] net-sysfs: move the xps cpus/rxqs
 retrieval in a common function

On Mon, Feb 8, 2021 at 9:19 AM Antoine Tenart <atenart@...nel.org> wrote:
>
> Most of the xps_cpus_show and xps_rxqs_show functions share the same
> logic. Having it in two different functions does not help maintenance.
> This patch moves their common logic into a new function, xps_queue_show,
> to improve this.
>
> Signed-off-by: Antoine Tenart <atenart@...nel.org>
> ---
>  net/core/net-sysfs.c | 98 ++++++++++++++------------------------------
>  1 file changed, 31 insertions(+), 67 deletions(-)
>
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index 6ce5772e799e..984c15248483 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -1314,35 +1314,31 @@ static const struct attribute_group dql_group = {
>  #endif /* CONFIG_BQL */
>
>  #ifdef CONFIG_XPS
> -static ssize_t xps_cpus_show(struct netdev_queue *queue,
> -                            char *buf)
> +static ssize_t xps_queue_show(struct net_device *dev, unsigned int index,
> +                             char *buf, enum xps_map_type type)
>  {
> -       struct net_device *dev = queue->dev;
>         struct xps_dev_maps *dev_maps;
> -       unsigned int index, nr_ids;
> -       int j, len, ret, tc = 0;
>         unsigned long *mask;
> -
> -       if (!netif_is_multiqueue(dev))
> -               return -ENOENT;
> -
> -       index = get_netdev_queue_index(queue);
> -
> -       /* If queue belongs to subordinate dev use its map */
> -       dev = netdev_get_tx_queue(dev, index)->sb_dev ? : dev;
> +       unsigned int nr_ids;
> +       int j, len, tc = 0;
>
>         tc = netdev_txq_to_tc(dev, index);
>         if (tc < 0)
>                 return -EINVAL;
>
>         rcu_read_lock();
> -       dev_maps = rcu_dereference(dev->xps_maps[XPS_CPUS]);
> -       nr_ids = dev_maps ? dev_maps->nr_ids : nr_cpu_ids;
> +       dev_maps = rcu_dereference(dev->xps_maps[type]);
> +
> +       /* Default to nr_cpu_ids/dev->num_rx_queues and do not just return 0
> +        * when dev_maps hasn't been allocated yet, to be backward compatible.
> +        */
> +       nr_ids = dev_maps ? dev_maps->nr_ids :
> +                (type == XPS_CPUS ? nr_cpu_ids : dev->num_rx_queues);
>
>         mask = bitmap_zalloc(nr_ids, GFP_KERNEL);
>         if (!mask) {
> -               ret = -ENOMEM;
> -               goto err_rcu_unlock;
> +               rcu_read_unlock();
> +               return -ENOMEM;
>         }
>
>         if (!dev_maps || tc >= dev_maps->num_tc)
> @@ -1368,11 +1364,24 @@ static ssize_t xps_cpus_show(struct netdev_queue *queue,
>
>         len = bitmap_print_to_pagebuf(false, buf, mask, nr_ids);
>         bitmap_free(mask);
> +
>         return len < PAGE_SIZE ? len : -EINVAL;
> +}
>
> -err_rcu_unlock:
> -       rcu_read_unlock();
> -       return ret;
> +static ssize_t xps_cpus_show(struct netdev_queue *queue, char *buf)
> +{
> +       struct net_device *dev = queue->dev;
> +       unsigned int index;
> +
> +       if (!netif_is_multiqueue(dev))
> +               return -ENOENT;
> +
> +       index = get_netdev_queue_index(queue);
> +
> +       /* If queue belongs to subordinate dev use its map */
> +       dev = netdev_get_tx_queue(dev, index)->sb_dev ? : dev;
> +
> +       return xps_queue_show(dev, index, buf, XPS_CPUS);
>  }
>
>  static ssize_t xps_cpus_store(struct netdev_queue *queue,

So this patch has the same issue as the one that was removing the
rtnl_lock. Basically the sb_dev needs to still be protected by the
rtnl_lock. We might need to take the rtnl_lock and maybe make use of
the get_device/put_device logic to make certain the device cannot be
freed while you are passing it to xps_queue_show.