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Date: Mon, 21 Dec 2020 14:33:15 -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>, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net v2 2/3] net: move the xps cpus retrieval out of net-sysfs
On Mon, Dec 21, 2020 at 11:36 AM Antoine Tenart <atenart@...nel.org> wrote:
>
> Accesses to dev->xps_cpus_map (when using dev->num_tc) should be
> protected by the xps_map mutex, to avoid possible race conditions when
> dev->num_tc is updated while the map is accessed. This patch moves the
> logic accessing dev->xps_cpu_map and dev->num_tc to net/core/dev.c,
> where the xps_map mutex is defined and used.
>
> Fixes: 184c449f91fe ("net: Add support for XPS with QoS via traffic classes")
> Signed-off-by: Antoine Tenart <atenart@...nel.org>
It is a bit of a shame that we have to use the mutex_lock while just
displaying the table. But we end up needing it if we are going to use
the xps_map_mutex to protect us from the num_tc being updated while we
are reading it.
One thing I might change is to actually bump this patch up in the
patch set as I think it would probably make things a bit cleaner to
read as you are going to be moving the other functions to this pattern
as well.
> ---
> include/linux/netdevice.h | 8 ++++++
> net/core/dev.c | 59 +++++++++++++++++++++++++++++++++++++++
> net/core/net-sysfs.c | 54 ++++++++---------------------------
> 3 files changed, 79 insertions(+), 42 deletions(-)
>
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 259be67644e3..bfd6cfa3ea90 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -3671,6 +3671,8 @@ int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,
> u16 index);
> int __netif_set_xps_queue(struct net_device *dev, const unsigned long *mask,
> u16 index, bool is_rxqs_map);
> +int netif_show_xps_queue(struct net_device *dev, unsigned long **mask,
> + u16 index);
>
> /**
> * netif_attr_test_mask - Test a CPU or Rx queue set in a mask
> @@ -3769,6 +3771,12 @@ static inline int __netif_set_xps_queue(struct net_device *dev,
> {
> return 0;
> }
> +
> +static inline int netif_show_xps_queue(struct net_device *dev,
> + unsigned long **mask, u16 index)
> +{
> + return 0;
> +}
> #endif
>
> /**
> diff --git a/net/core/dev.c b/net/core/dev.c
> index effdb7fee9df..a0257da4160a 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2831,6 +2831,65 @@ int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,
> }
> EXPORT_SYMBOL(netif_set_xps_queue);
>
> +int netif_show_xps_queue(struct net_device *dev, unsigned long **mask,
> + u16 index)
> +{
> + const unsigned long *possible_mask = NULL;
> + int j, num_tc = 1, tc = 0, ret = 0;
> + struct xps_dev_maps *dev_maps;
> + unsigned int nr_ids;
> +
> + rcu_read_lock();
> + mutex_lock(&xps_map_mutex);
> +
So you only need to call mutex_lock here. The rcu_read_lock becomes redundant.
> + if (dev->num_tc) {
> + num_tc = dev->num_tc;
> + if (num_tc < 0) {
> + ret = -EINVAL;
> + goto out_no_map;
> + }
> +
> + /* If queue belongs to subordinate dev use its map */
> + dev = netdev_get_tx_queue(dev, index)->sb_dev ? : dev;
> +
> + tc = netdev_txq_to_tc(dev, index);
> + if (tc < 0) {
> + ret = -EINVAL;
> + goto out_no_map;
> + }
> + }
> +
> + dev_maps = rcu_dereference(dev->xps_cpus_map);
> + if (!dev_maps)
> + goto out_no_map;
> + nr_ids = nr_cpu_ids;
> + if (num_possible_cpus() > 1)
> + possible_mask = cpumask_bits(cpu_possible_mask);
> +
> + for (j = -1; j = netif_attrmask_next(j, possible_mask, nr_ids),
> + j < nr_ids;) {
> + int i, tci = j * num_tc + tc;
> + struct xps_map *map;
> +
> + map = rcu_dereference(dev_maps->attr_map[tci]);
For this you can use either rcu_dereference_protected, or you can use
xmap_dereference.
> + if (!map)
> + continue;
> +
> + for (i = map->len; i--;) {
> + if (map->queues[i] == index) {
> + set_bit(j, *mask);
> + break;
> + }
> + }
> + }
> +
> +out_no_map:
> + mutex_unlock(&xps_map_mutex);
> + rcu_read_unlock();
> +
> + return ret;
> +}
> +EXPORT_SYMBOL(netif_show_xps_queue);
> #endif
>
> static void __netdev_unbind_sb_channel(struct net_device *dev,
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index 999b70c59761..29ee69b67972 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -1314,60 +1314,30 @@ 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_cpus_show(struct netdev_queue *queue, char *buf)
> {
> struct net_device *dev = queue->dev;
> - int cpu, len, num_tc = 1, tc = 0;
> - struct xps_dev_maps *dev_maps;
> - cpumask_var_t mask;
> - unsigned long index;
> + unsigned long *mask, index;
> + int len, ret;
>
> if (!netif_is_multiqueue(dev))
> return -ENOENT;
>
> index = get_netdev_queue_index(queue);
>
> - if (dev->num_tc) {
> - /* Do not allow XPS on subordinate device directly */
> - num_tc = dev->num_tc;
> - if (num_tc < 0)
> - return -EINVAL;
> -
> - /* If queue belongs to subordinate dev use its map */
> - dev = netdev_get_tx_queue(dev, index)->sb_dev ? : dev;
> -
> - tc = netdev_txq_to_tc(dev, index);
> - if (tc < 0)
> - return -EINVAL;
> - }
> -
> - if (!zalloc_cpumask_var(&mask, GFP_KERNEL))
> + mask = bitmap_zalloc(nr_cpu_ids, GFP_KERNEL);
> + if (!mask)
> return -ENOMEM;
>
> - rcu_read_lock();
> - dev_maps = rcu_dereference(dev->xps_cpus_map);
> - if (dev_maps) {
> - for_each_possible_cpu(cpu) {
> - int i, tci = cpu * num_tc + tc;
> - struct xps_map *map;
> -
> - map = rcu_dereference(dev_maps->attr_map[tci]);
> - if (!map)
> - continue;
> -
> - for (i = map->len; i--;) {
> - if (map->queues[i] == index) {
> - cpumask_set_cpu(cpu, mask);
> - break;
> - }
> - }
> - }
> + ret = netif_show_xps_queue(dev, &mask, index);
> + if (ret) {
> + bitmap_free(mask);
> + return ret;
> }
> - rcu_read_unlock();
>
> - len = snprintf(buf, PAGE_SIZE, "%*pb\n", cpumask_pr_args(mask));
> - free_cpumask_var(mask);
> + len = bitmap_print_to_pagebuf(false, buf, mask, nr_cpu_ids);
> + bitmap_free(mask);
> +
> return len < PAGE_SIZE ? len : -EINVAL;
> }
>
> --
> 2.29.2
>
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