virtio: console: Add reference counting for port struct
When a port got hot-unplugged, when a port was open, any file operation
after the unplugging resulted in a crash. This is fixed by ref-counting
the port structure, and releasing it only when the file is closed.
This splits the unplug operation in two parts: first marks the port
as unavailable, removes all the buffers in the vqs and removes the port
from the per-device list of ports. The second stage, invoked when all
references drop to zero, releases the chardev and frees all other memory.
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 8a9c140..288701c 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -187,6 +187,9 @@
struct cdev *cdev;
struct device *dev;
+ /* Reference-counting to handle port hot-unplugs and file operations */
+ struct kref kref;
+
/* A waitqueue for poll() or blocking read operations */
wait_queue_head_t waitqueue;
@@ -725,6 +728,8 @@
return ret;
}
+static void remove_port(struct kref *kref);
+
static int port_fops_release(struct inode *inode, struct file *filp)
{
struct port *port;
@@ -745,6 +750,16 @@
reclaim_consumed_buffers(port);
spin_unlock_irq(&port->outvq_lock);
+ /*
+ * Locks aren't necessary here as a port can't be opened after
+ * unplug, and if a port isn't unplugged, a kref would already
+ * exist for the port. Plus, taking ports_lock here would
+ * create a dependency on other locks taken by functions
+ * inside remove_port if we're the last holder of the port,
+ * creating many problems.
+ */
+ kref_put(&port->kref, remove_port);
+
return 0;
}
@@ -757,6 +772,11 @@
port = find_port_by_devt(cdev->dev);
filp->private_data = port;
+ /* Prevent against a port getting hot-unplugged at the same time */
+ spin_lock_irq(&port->portdev->ports_lock);
+ kref_get(&port->kref);
+ spin_unlock_irq(&port->portdev->ports_lock);
+
/*
* Don't allow opening of console port devices -- that's done
* via /dev/hvc
@@ -791,6 +811,7 @@
return 0;
out:
+ kref_put(&port->kref, remove_port);
return ret;
}
@@ -1079,6 +1100,7 @@
err = -ENOMEM;
goto fail;
}
+ kref_init(&port->kref);
port->portdev = portdev;
port->id = id;
@@ -1183,22 +1205,43 @@
return err;
}
-/* Remove all port-specific data. */
-static void remove_port(struct port *port)
+/* No users remain, remove all port-specific data. */
+static void remove_port(struct kref *kref)
+{
+ struct port *port;
+
+ port = container_of(kref, struct port, kref);
+
+ sysfs_remove_group(&port->dev->kobj, &port_attribute_group);
+ device_destroy(pdrvdata.class, port->dev->devt);
+ cdev_del(port->cdev);
+
+ kfree(port->name);
+
+ debugfs_remove(port->debugfs_file);
+
+ kfree(port);
+}
+
+/*
+ * Port got unplugged. Remove port from portdev's list and drop the
+ * kref reference. If no userspace has this port opened, it will
+ * result in immediate removal the port.
+ */
+static void unplug_port(struct port *port)
{
struct port_buffer *buf;
+ spin_lock_irq(&port->portdev->ports_lock);
+ list_del(&port->list);
+ spin_unlock_irq(&port->portdev->ports_lock);
+
if (port->guest_connected) {
port->guest_connected = false;
port->host_connected = false;
wake_up_interruptible(&port->waitqueue);
- send_control_msg(port, VIRTIO_CONSOLE_PORT_OPEN, 0);
}
- spin_lock_irq(&port->portdev->ports_lock);
- list_del(&port->list);
- spin_unlock_irq(&port->portdev->ports_lock);
-
if (is_console_port(port)) {
spin_lock_irq(&pdrvdata_lock);
list_del(&port->cons.list);
@@ -1216,9 +1259,6 @@
hvc_remove(port->cons.hvc);
#endif
}
- sysfs_remove_group(&port->dev->kobj, &port_attribute_group);
- device_destroy(pdrvdata.class, port->dev->devt);
- cdev_del(port->cdev);
/* Remove unused data this port might have received. */
discard_port_data(port);
@@ -1229,11 +1269,19 @@
while ((buf = virtqueue_detach_unused_buf(port->in_vq)))
free_buf(buf);
- kfree(port->name);
+ /*
+ * We should just assume the device itself has gone off --
+ * else a close on an open port later will try to send out a
+ * control message.
+ */
+ port->portdev = NULL;
- debugfs_remove(port->debugfs_file);
-
- kfree(port);
+ /*
+ * Locks around here are not necessary - a port can't be
+ * opened after we removed the port struct from ports_list
+ * above.
+ */
+ kref_put(&port->kref, remove_port);
}
/* Any private messages that the Host and Guest want to share */
@@ -1272,7 +1320,7 @@
add_port(portdev, cpkt->id);
break;
case VIRTIO_CONSOLE_PORT_REMOVE:
- remove_port(port);
+ unplug_port(port);
break;
case VIRTIO_CONSOLE_CONSOLE_PORT:
if (!cpkt->value)
@@ -1686,7 +1734,7 @@
cancel_work_sync(&portdev->control_work);
list_for_each_entry_safe(port, port2, &portdev->ports, list)
- remove_port(port);
+ unplug_port(port);
unregister_chrdev(portdev->chr_major, "virtio-portsdev");