net/vdpa: Use readers/writers semaphore instead of vdpa_dev_mutex

Use rw_semaphore instead of mutex to control access to vdpa devices.
This can be especially beneficial in case processes poll on statistics
information.
Suggested-by: Si-Wei Liu <si-wei.liu@oracle.com>
Reviewed-by: Si-Wei Liu <si-wei.liu@oracle.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Eli Cohen <elic@nvidia.com>
Message-Id: <20220518133804.1075129-4-elic@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

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;
 }
@@ -627,7 +627,7 @@ 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");
@@ -643,7 +643,7 @@ 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;
 }
 
@@ -659,7 +659,7 @@ 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");
@@ -677,7 +677,7 @@ 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;
 }
 
@@ -743,7 +743,7 @@ 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");
@@ -761,13 +761,13 @@ 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;
 }
@@ -809,9 +809,9 @@ 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;
 }
@@ -1031,7 +1031,7 @@ 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");
@@ -1052,7 +1052,7 @@ 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;
@@ -1090,9 +1090,9 @@ 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;
 }
@@ -1119,7 +1119,7 @@ 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");
@@ -1139,7 +1139,7 @@ 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;
 
@@ -1147,7 +1147,7 @@ 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;
 }