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virtio: console: Add reference counting for port struct

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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>
This commit is contained in:
Amit Shah 2010-09-02 18:38:29 +05:30 committed by Rusty Russell
parent d22a69892b
commit b353a6b821
1 changed files with 64 additions and 16 deletions
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80
drivers/char/virtio_console.c
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@ -187,6 +187,9 @@ struct port {
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 @@ static unsigned int port_fops_poll(struct file *filp, poll_table *wait)
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 @@ static int port_fops_release(struct inode *inode, struct file *filp)
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 @@ static int port_fops_open(struct inode *inode, struct file *filp)
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 @@ static int port_fops_open(struct inode *inode, struct file *filp)
return 0;
out:
kref_put(&port->kref, remove_port);
return ret;
}
@ -1079,6 +1100,7 @@ static int add_port(struct ports_device *portdev, u32 id)
err = -ENOMEM;
goto fail;
}
kref_init(&port->kref);
port->portdev = portdev;
port->id = id;
@ -1183,22 +1205,43 @@ fail:
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 @@ static void remove_port(struct port *port)
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 @@ static void remove_port(struct port *port)
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 @@ static void handle_control_message(struct ports_device *portdev,
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 @@ static void virtcons_remove(struct virtio_device *vdev)
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");