Commit 060eabe8 authored by SeongJae Park's avatar SeongJae Park Committed by Boris Ostrovsky
Browse files

xenbus/backend: Protect xenbus callback with lock 



A driver's 'reclaim_memory' callback can race with 'probe' or 'remove'
because it will be called whenever memory pressure is detected.  To
avoid such race, this commit embeds a spinlock in each 'xenbus_device'
and make 'xenbus' to hold the lock while the corresponded callbacks are
running.

Reviewed-by: default avatarJuergen Gross <jgross@suse.com>
Signed-off-by: default avatarSeongJae Park <sjpark@amazon.de>
Signed-off-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
parent 8a105678

drivers/xen/xenbus/xenbus_probe.c

+7 −1
Original line number Diff line number Diff line
@@ -239,7 +239,9 @@ int xenbus_dev_probe(struct device *_dev) 
		goto fail;

	}



	spin_lock(&dev->reclaim_lock);

	err = drv->probe(dev, id);

	spin_unlock(&dev->reclaim_lock);

	if (err)

		goto fail_put;
@@ -268,8 +270,11 @@ int xenbus_dev_remove(struct device *_dev) 


	free_otherend_watch(dev);



	if (drv->remove)

	if (drv->remove) {

		spin_lock(&dev->reclaim_lock);

		drv->remove(dev);

		spin_unlock(&dev->reclaim_lock);

	}



	module_put(drv->driver.owner);
@@ -468,6 +473,7 @@ int xenbus_probe_node(struct xen_bus_type *bus, 
		goto fail;



	dev_set_name(&xendev->dev, "%s", devname);

	spin_lock_init(&xendev->reclaim_lock);



	/* Register with generic device framework. */

	err = device_register(&xendev->dev);

drivers/xen/xenbus/xenbus_probe_backend.c

+8 −2
Original line number Diff line number Diff line
@@ -250,12 +250,18 @@ static int backend_probe_and_watch(struct notifier_block *notifier, 
static int backend_reclaim_memory(struct device *dev, void *data)

{

	const struct xenbus_driver *drv;

	struct xenbus_device *xdev;



	if (!dev->driver)

		return 0;

	drv = to_xenbus_driver(dev->driver);

	if (drv && drv->reclaim_memory)

		drv->reclaim_memory(to_xenbus_device(dev));

	if (drv && drv->reclaim_memory) {

		xdev = to_xenbus_device(dev);

		if (!spin_trylock(&xdev->reclaim_lock))

			return 0;

		drv->reclaim_memory(xdev);

		spin_unlock(&xdev->reclaim_lock);

	}

	return 0;

}

include/xen/xenbus.h

+1 −0
Original line number Diff line number Diff line
@@ -76,6 +76,7 @@ struct xenbus_device { 
	enum xenbus_state state;

	struct completion down;

	struct work_struct work;

	spinlock_t reclaim_lock;

};



static inline struct xenbus_device *to_xenbus_device(struct device *dev)

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