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From:   Eli Cohen <elic@nvidia.com>
To:     <mst@redhat.com>, <jasowang@redhat.com>
CC:     <virtualization@lists.linux-foundation.org>,
        <linux-kernel@vger.kernel.org>, <si-wei.liu@oracle.com>,
        Eli Cohen <elic@nvidia.com>
Subject: [PATCH] net/vdpa: Use reader/writers semaphore instead of mutex
Date:   Wed, 11 May 2022 15:58:45 +0300
Message-ID: <20220511125845.1332586-1-elic@nvidia.com>
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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>
---
 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