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References: <20220511125845.1332586-1-elic@nvidia.com>
In-Reply-To: <20220511125845.1332586-1-elic@nvidia.com>
From:   Jason Wang <jasowang@redhat.com>
Date:   Thu, 12 May 2022 12:14:07 +0800
Message-ID: <CACGkMEtGvGM7JzP+xHZyxyOFL+wzLPa6-XgfOvM=1ZEf1NqKUg@mail.gmail.com>
Subject: Re: [PATCH] net/vdpa: Use reader/writers semaphore instead of mutex
To:     Eli Cohen <elic@nvidia.com>
Cc:     mst <mst@redhat.com>,
        virtualization <virtualization@lists.linux-foundation.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Si-Wei Liu <si-wei.liu@oracle.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Wed, May 11, 2022 at 8:58 PM Eli Cohen <elic@nvidia.com> wrote:
>
> Use rw_semaphore instead of mutex to control access to vdpa devices.
> This can be especially beneficial in case process poll on statistics
> information.
>
> Suggested-by: Si-Wei Liu <si-wei.liu@oracle.com>
> Signed-off-by: Eli Cohen <elic@nvidia.com>

Acked-by: Jason Wang <jasowang@redhat.com>

> ---
>  drivers/vdpa/vdpa.c | 64 ++++++++++++++++++++++-----------------------
>  1 file changed, 32 insertions(+), 32 deletions(-)
>
> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> index 0fb4a615f267..ced634f94f76 100644
> --- a/drivers/vdpa/vdpa.c
> +++ b/drivers/vdpa/vdpa.c
> @@ -18,7 +18,7 @@
>
>  static LIST_HEAD(mdev_head);
>  /* A global mutex that protects vdpa management device and device level operations. */
> -static DEFINE_MUTEX(vdpa_dev_mutex);
> +static DECLARE_RWSEM(vdpa_dev_lock);
>  static DEFINE_IDA(vdpa_index_ida);
>
>  void vdpa_set_status(struct vdpa_device *vdev, u8 status)
> @@ -238,7 +238,7 @@ static int __vdpa_register_device(struct vdpa_device *vdev, u32 nvqs)
>
>         vdev->nvqs = nvqs;
>
> -       lockdep_assert_held(&vdpa_dev_mutex);
> +       lockdep_assert_held(&vdpa_dev_lock);
>         dev = bus_find_device(&vdpa_bus, NULL, dev_name(&vdev->dev), vdpa_name_match);
>         if (dev) {
>                 put_device(dev);
> @@ -278,9 +278,9 @@ int vdpa_register_device(struct vdpa_device *vdev, u32 nvqs)
>  {
>         int err;
>
> -       mutex_lock(&vdpa_dev_mutex);
> +       down_write(&vdpa_dev_lock);
>         err = __vdpa_register_device(vdev, nvqs);
> -       mutex_unlock(&vdpa_dev_mutex);
> +       up_write(&vdpa_dev_lock);
>         return err;
>  }
>  EXPORT_SYMBOL_GPL(vdpa_register_device);
> @@ -293,7 +293,7 @@ EXPORT_SYMBOL_GPL(vdpa_register_device);
>   */
>  void _vdpa_unregister_device(struct vdpa_device *vdev)
>  {
> -       lockdep_assert_held(&vdpa_dev_mutex);
> +       lockdep_assert_held(&vdpa_dev_lock);
>         WARN_ON(!vdev->mdev);
>         device_unregister(&vdev->dev);
>  }
> @@ -305,9 +305,9 @@ EXPORT_SYMBOL_GPL(_vdpa_unregister_device);
>   */
>  void vdpa_unregister_device(struct vdpa_device *vdev)
>  {
> -       mutex_lock(&vdpa_dev_mutex);
> +       down_write(&vdpa_dev_lock);
>         device_unregister(&vdev->dev);
> -       mutex_unlock(&vdpa_dev_mutex);
> +       up_write(&vdpa_dev_lock);
>  }
>  EXPORT_SYMBOL_GPL(vdpa_unregister_device);
>
> @@ -352,9 +352,9 @@ int vdpa_mgmtdev_register(struct vdpa_mgmt_dev *mdev)
>                 return -EINVAL;
>
>         INIT_LIST_HEAD(&mdev->list);
> -       mutex_lock(&vdpa_dev_mutex);
> +       down_write(&vdpa_dev_lock);
>         list_add_tail(&mdev->list, &mdev_head);
> -       mutex_unlock(&vdpa_dev_mutex);
> +       up_write(&vdpa_dev_lock);
>         return 0;
>  }
>  EXPORT_SYMBOL_GPL(vdpa_mgmtdev_register);
> @@ -371,14 +371,14 @@ static int vdpa_match_remove(struct device *dev, void *data)
>
>  void vdpa_mgmtdev_unregister(struct vdpa_mgmt_dev *mdev)
>  {
> -       mutex_lock(&vdpa_dev_mutex);
> +       down_write(&vdpa_dev_lock);
>
>         list_del(&mdev->list);
>
>         /* Filter out all the entries belong to this management device and delete it. */
>         bus_for_each_dev(&vdpa_bus, NULL, mdev, vdpa_match_remove);
>
> -       mutex_unlock(&vdpa_dev_mutex);
> +       up_write(&vdpa_dev_lock);
>  }
>  EXPORT_SYMBOL_GPL(vdpa_mgmtdev_unregister);
>
> @@ -532,17 +532,17 @@ static int vdpa_nl_cmd_mgmtdev_get_doit(struct sk_buff *skb, struct genl_info *i
>         if (!msg)
>                 return -ENOMEM;
>
> -       mutex_lock(&vdpa_dev_mutex);
> +       down_read(&vdpa_dev_lock);
>         mdev = vdpa_mgmtdev_get_from_attr(info->attrs);
>         if (IS_ERR(mdev)) {
> -               mutex_unlock(&vdpa_dev_mutex);
> +               up_read(&vdpa_dev_lock);
>                 NL_SET_ERR_MSG_MOD(info->extack, "Fail to find the specified mgmt device");
>                 err = PTR_ERR(mdev);
>                 goto out;
>         }
>
>         err = vdpa_mgmtdev_fill(mdev, msg, info->snd_portid, info->snd_seq, 0);
> -       mutex_unlock(&vdpa_dev_mutex);
> +       up_read(&vdpa_dev_lock);
>         if (err)
>                 goto out;
>         err = genlmsg_reply(msg, info);
> @@ -561,7 +561,7 @@ vdpa_nl_cmd_mgmtdev_get_dumpit(struct sk_buff *msg, struct netlink_callback *cb)
>         int idx = 0;
>         int err;
>
> -       mutex_lock(&vdpa_dev_mutex);
> +       down_read(&vdpa_dev_lock);
>         list_for_each_entry(mdev, &mdev_head, list) {
>                 if (idx < start) {
>                         idx++;
> @@ -574,7 +574,7 @@ vdpa_nl_cmd_mgmtdev_get_dumpit(struct sk_buff *msg, struct netlink_callback *cb)
>                 idx++;
>         }
>  out:
> -       mutex_unlock(&vdpa_dev_mutex);
> +       up_read(&vdpa_dev_lock);
>         cb->args[0] = idx;
>         return msg->len;
>  }
> @@ -630,7 +630,7 @@ static int vdpa_nl_cmd_dev_add_set_doit(struct sk_buff *skb, struct genl_info *i
>             !netlink_capable(skb, CAP_NET_ADMIN))
>                 return -EPERM;
>
> -       mutex_lock(&vdpa_dev_mutex);
> +       down_write(&vdpa_dev_lock);
>         mdev = vdpa_mgmtdev_get_from_attr(info->attrs);
>         if (IS_ERR(mdev)) {
>                 NL_SET_ERR_MSG_MOD(info->extack, "Fail to find the specified management device");
> @@ -650,7 +650,7 @@ static int vdpa_nl_cmd_dev_add_set_doit(struct sk_buff *skb, struct genl_info *i
>
>         err = mdev->ops->dev_add(mdev, name, &config);
>  err:
> -       mutex_unlock(&vdpa_dev_mutex);
> +       up_write(&vdpa_dev_lock);
>         return err;
>  }
>
> @@ -666,7 +666,7 @@ static int vdpa_nl_cmd_dev_del_set_doit(struct sk_buff *skb, struct genl_info *i
>                 return -EINVAL;
>         name = nla_data(info->attrs[VDPA_ATTR_DEV_NAME]);
>
> -       mutex_lock(&vdpa_dev_mutex);
> +       down_write(&vdpa_dev_lock);
>         dev = bus_find_device(&vdpa_bus, NULL, name, vdpa_name_match);
>         if (!dev) {
>                 NL_SET_ERR_MSG_MOD(info->extack, "device not found");
> @@ -684,7 +684,7 @@ static int vdpa_nl_cmd_dev_del_set_doit(struct sk_buff *skb, struct genl_info *i
>  mdev_err:
>         put_device(dev);
>  dev_err:
> -       mutex_unlock(&vdpa_dev_mutex);
> +       up_write(&vdpa_dev_lock);
>         return err;
>  }
>
> @@ -750,7 +750,7 @@ static int vdpa_nl_cmd_dev_get_doit(struct sk_buff *skb, struct genl_info *info)
>         if (!msg)
>                 return -ENOMEM;
>
> -       mutex_lock(&vdpa_dev_mutex);
> +       down_read(&vdpa_dev_lock);
>         dev = bus_find_device(&vdpa_bus, NULL, devname, vdpa_name_match);
>         if (!dev) {
>                 NL_SET_ERR_MSG_MOD(info->extack, "device not found");
> @@ -768,13 +768,13 @@ static int vdpa_nl_cmd_dev_get_doit(struct sk_buff *skb, struct genl_info *info)
>
>         err = genlmsg_reply(msg, info);
>         put_device(dev);
> -       mutex_unlock(&vdpa_dev_mutex);
> +       up_read(&vdpa_dev_lock);
>         return err;
>
>  mdev_err:
>         put_device(dev);
>  err:
> -       mutex_unlock(&vdpa_dev_mutex);
> +       up_read(&vdpa_dev_lock);
>         nlmsg_free(msg);
>         return err;
>  }
> @@ -816,9 +816,9 @@ static int vdpa_nl_cmd_dev_get_dumpit(struct sk_buff *msg, struct netlink_callba
>         info.start_idx = cb->args[0];
>         info.idx = 0;
>
> -       mutex_lock(&vdpa_dev_mutex);
> +       down_read(&vdpa_dev_lock);
>         bus_for_each_dev(&vdpa_bus, NULL, &info, vdpa_dev_dump);
> -       mutex_unlock(&vdpa_dev_mutex);
> +       up_read(&vdpa_dev_lock);
>         cb->args[0] = info.idx;
>         return msg->len;
>  }
> @@ -1016,7 +1016,7 @@ static int vdpa_nl_cmd_dev_config_get_doit(struct sk_buff *skb, struct genl_info
>         if (!msg)
>                 return -ENOMEM;
>
> -       mutex_lock(&vdpa_dev_mutex);
> +       down_read(&vdpa_dev_lock);
>         dev = bus_find_device(&vdpa_bus, NULL, devname, vdpa_name_match);
>         if (!dev) {
>                 NL_SET_ERR_MSG_MOD(info->extack, "device not found");
> @@ -1037,7 +1037,7 @@ static int vdpa_nl_cmd_dev_config_get_doit(struct sk_buff *skb, struct genl_info
>  mdev_err:
>         put_device(dev);
>  dev_err:
> -       mutex_unlock(&vdpa_dev_mutex);
> +       up_read(&vdpa_dev_lock);
>         if (err)
>                 nlmsg_free(msg);
>         return err;
> @@ -1075,9 +1075,9 @@ vdpa_nl_cmd_dev_config_get_dumpit(struct sk_buff *msg, struct netlink_callback *
>         info.start_idx = cb->args[0];
>         info.idx = 0;
>
> -       mutex_lock(&vdpa_dev_mutex);
> +       down_read(&vdpa_dev_lock);
>         bus_for_each_dev(&vdpa_bus, NULL, &info, vdpa_dev_config_dump);
> -       mutex_unlock(&vdpa_dev_mutex);
> +       up_read(&vdpa_dev_lock);
>         cb->args[0] = info.idx;
>         return msg->len;
>  }
> @@ -1104,7 +1104,7 @@ static int vdpa_nl_cmd_dev_stats_get_doit(struct sk_buff *skb,
>                 return -ENOMEM;
>
>         index = nla_get_u32(info->attrs[VDPA_ATTR_DEV_QUEUE_INDEX]);
> -       mutex_lock(&vdpa_dev_mutex);
> +       down_read(&vdpa_dev_lock);
>         dev = bus_find_device(&vdpa_bus, NULL, devname, vdpa_name_match);
>         if (!dev) {
>                 NL_SET_ERR_MSG_MOD(info->extack, "device not found");
> @@ -1124,7 +1124,7 @@ static int vdpa_nl_cmd_dev_stats_get_doit(struct sk_buff *skb,
>         err = genlmsg_reply(msg, info);
>
>         put_device(dev);
> -       mutex_unlock(&vdpa_dev_mutex);
> +       up_read(&vdpa_dev_lock);
>
>         return err;
>
> @@ -1132,7 +1132,7 @@ static int vdpa_nl_cmd_dev_stats_get_doit(struct sk_buff *skb,
>         put_device(dev);
>  dev_err:
>         nlmsg_free(msg);
> -       mutex_unlock(&vdpa_dev_mutex);
> +       up_read(&vdpa_dev_lock);
>         return err;
>  }
>
> --
> 2.35.1
>