[PATCH 3/4] Drivers: hv: utils: introduce HVUTIL_TRANSPORT_DESTROY mode

[Vitaly Kuznetsov <vkuznets@redhat.com>]

When Hyper-V host asks us to remove some util driver by closing the
appropriate channel there is no easy way to force the current file
descriptor holder to hang up but we can start to respond -EBADF to all
operations asking it to exit gracefully.

As we're setting hvt->mode from two separate contexts now we need to use
a proper locking.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 drivers/hv/hv_utils_transport.c | 69 ++++++++++++++++++++++++++++++++---------
 drivers/hv/hv_utils_transport.h |  1 +
 2 files changed, 56 insertions(+), 14 deletions(-)

diff --git a/drivers/hv/hv_utils_transport.c b/drivers/hv/hv_utils_transport.c
index 5cce2d2..984cba5 100644
--- a/drivers/hv/hv_utils_transport.c
+++ b/drivers/hv/hv_utils_transport.c
@@ -27,11 +27,9 @@ static struct list_head hvt_list = LIST_HEAD_INIT(hvt_list);
 
 static void hvt_reset(struct hvutil_transport *hvt)
 {
-	mutex_lock(&hvt->lock);
 	kfree(hvt->outmsg);
 	hvt->outmsg = NULL;
 	hvt->outmsg_len = 0;
-	mutex_unlock(&hvt->lock);
 	if (hvt->on_reset)
 		hvt->on_reset();
 }
@@ -44,10 +42,17 @@ static ssize_t hvt_op_read(struct file *file, char __user *buf,
 
 	hvt = container_of(file->f_op, struct hvutil_transport, fops);
 
-	if (wait_event_interruptible(hvt->outmsg_q, hvt->outmsg_len > 0))
+	if (wait_event_interruptible(hvt->outmsg_q, hvt->outmsg_len > 0 ||
+				     hvt->mode != HVUTIL_TRANSPORT_CHARDEV))
 		return -EINTR;
 
 	mutex_lock(&hvt->lock);
+
+	if (hvt->mode == HVUTIL_TRANSPORT_DESTROY) {
+		ret = -EBADF;
+		goto out_unlock;
+	}
+
 	if (!hvt->outmsg) {
 		ret = -EAGAIN;
 		goto out_unlock;
@@ -85,6 +90,9 @@ static ssize_t hvt_op_write(struct file *file, const char __user *buf,
 	if (IS_ERR(inmsg))
 		return PTR_ERR(inmsg);
 
+	if (hvt->mode == HVUTIL_TRANSPORT_DESTROY)
+		return -EBADF;
+
 	if (hvt->on_msg(inmsg, count))
 		ret = -EFAULT;
 	kfree(inmsg);
@@ -99,6 +107,10 @@ static unsigned int hvt_op_poll(struct file *file, poll_table *wait)
 	hvt = container_of(file->f_op, struct hvutil_transport, fops);
 
 	poll_wait(file, &hvt->outmsg_q, wait);
+
+	if (hvt->mode == HVUTIL_TRANSPORT_DESTROY)
+		return -EBADF;
+
 	if (hvt->outmsg_len > 0)
 		return POLLIN | POLLRDNORM;
 
@@ -108,26 +120,39 @@ static unsigned int hvt_op_poll(struct file *file, poll_table *wait)
 static int hvt_op_open(struct inode *inode, struct file *file)
 {
 	struct hvutil_transport *hvt;
+	int ret = 0;
+	bool issue_reset = false;
 
 	hvt = container_of(file->f_op, struct hvutil_transport, fops);
 
-	/*
-	 * Switching to CHARDEV mode. We switch bach to INIT when device
-	 * gets released.
-	 */
-	if (hvt->mode == HVUTIL_TRANSPORT_INIT)
+	mutex_lock(&hvt->lock);
+
+	if (hvt->mode == HVUTIL_TRANSPORT_DESTROY) {
+		ret = -EBADF;
+	} else if (hvt->mode == HVUTIL_TRANSPORT_INIT) {
+		/*
+		 * Switching to CHARDEV mode. We switch bach to INIT when
+		 * device gets released.
+		 */
 		hvt->mode = HVUTIL_TRANSPORT_CHARDEV;
+	}
 	else if (hvt->mode == HVUTIL_TRANSPORT_NETLINK) {
 		/*
 		 * We're switching from netlink communication to using char
 		 * device. Issue the reset first.
 		 */
-		hvt_reset(hvt);
+		issue_reset = true;
 		hvt->mode = HVUTIL_TRANSPORT_CHARDEV;
-	} else
-		return -EBUSY;
+	} else {
+		ret = -EBUSY;
+	}
 
-	return 0;
+	if (issue_reset)
+		hvt_reset(hvt);
+
+	mutex_unlock(&hvt->lock);
+
+	return ret;
 }
 
 static int hvt_op_release(struct inode *inode, struct file *file)
@@ -136,12 +161,15 @@ static int hvt_op_release(struct inode *inode, struct file *file)
 
 	hvt = container_of(file->f_op, struct hvutil_transport, fops);
 
-	hvt->mode = HVUTIL_TRANSPORT_INIT;
+	mutex_lock(&hvt->lock);
+	if (hvt->mode != HVUTIL_TRANSPORT_DESTROY)
+		hvt->mode = HVUTIL_TRANSPORT_INIT;
 	/*
 	 * Cleanup message buffers to avoid spurious messages when the daemon
 	 * connects back.
 	 */
 	hvt_reset(hvt);
+	mutex_unlock(&hvt->lock);
 
 	return 0;
 }
@@ -168,6 +196,7 @@ static void hvt_cn_callback(struct cn_msg *msg, struct netlink_skb_parms *nsp)
 	 * Switching to NETLINK mode. Switching to CHARDEV happens when someone
 	 * opens the device.
 	 */
+	mutex_lock(&hvt->lock);
 	if (hvt->mode == HVUTIL_TRANSPORT_INIT)
 		hvt->mode = HVUTIL_TRANSPORT_NETLINK;
 
@@ -175,6 +204,7 @@ static void hvt_cn_callback(struct cn_msg *msg, struct netlink_skb_parms *nsp)
 		hvt_found->on_msg(msg->data, msg->len);
 	else
 		pr_warn("hvt_cn_callback: unexpected netlink message!\n");
+	mutex_unlock(&hvt->lock);
 }
 
 int hvutil_transport_send(struct hvutil_transport *hvt, void *msg, int len)
@@ -182,7 +212,8 @@ int hvutil_transport_send(struct hvutil_transport *hvt, void *msg, int len)
 	struct cn_msg *cn_msg;
 	int ret = 0;
 
-	if (hvt->mode == HVUTIL_TRANSPORT_INIT) {
+	if (hvt->mode == HVUTIL_TRANSPORT_INIT ||
+	    hvt->mode == HVUTIL_TRANSPORT_DESTROY) {
 		return -EINVAL;
 	} else if (hvt->mode == HVUTIL_TRANSPORT_NETLINK) {
 		cn_msg = kzalloc(sizeof(*cn_msg) + len, GFP_ATOMIC);
@@ -198,6 +229,11 @@ int hvutil_transport_send(struct hvutil_transport *hvt, void *msg, int len)
 	}
 	/* HVUTIL_TRANSPORT_CHARDEV */
 	mutex_lock(&hvt->lock);
+	if (hvt->mode != HVUTIL_TRANSPORT_CHARDEV) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
 	if (hvt->outmsg) {
 		/* Previous message wasn't received */
 		ret = -EFAULT;
@@ -268,6 +304,11 @@ err_free_hvt:
 
 void hvutil_transport_destroy(struct hvutil_transport *hvt)
 {
+	mutex_lock(&hvt->lock);
+	hvt->mode = HVUTIL_TRANSPORT_DESTROY;
+	wake_up_interruptible(&hvt->outmsg_q);
+	mutex_unlock(&hvt->lock);
+
 	spin_lock(&hvt_list_lock);
 	list_del(&hvt->list);
 	spin_unlock(&hvt_list_lock);
diff --git a/drivers/hv/hv_utils_transport.h b/drivers/hv/hv_utils_transport.h
index bff4c92..06254a1 100644
--- a/drivers/hv/hv_utils_transport.h
+++ b/drivers/hv/hv_utils_transport.h
@@ -25,6 +25,7 @@ enum hvutil_transport_mode {
 	HVUTIL_TRANSPORT_INIT = 0,
 	HVUTIL_TRANSPORT_NETLINK,
 	HVUTIL_TRANSPORT_CHARDEV,
+	HVUTIL_TRANSPORT_DESTROY,
 };
 
 struct hvutil_transport {
-- 
2.4.3