Re: [PATCH] net/vdpa: Use reader/writers semaphore instead of mutex

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On 5/11/2022 5:58 AM, Eli Cohen 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@xxxxxxxxxx>
Signed-off-by: Eli Cohen <elic@xxxxxxxxxx>
LGTM. It might be good to pack this patch into the vendor stat series such that the newly added vdpa_dev_vendor_stats_fill() may use rw_semaphore on top. 

Reviewed-by: Si-Wei Liu <si-wei.liu@xxxxxxxxxx>


---
  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;
  }


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