[PATCH v14 2/5] xenbus/backend: Protect xenbus callback with lock

sjpark
2020-01-27T08:18:56Z

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: Juergen Gross <jgross@suse.com>
Signed-off-by: SeongJae Park <sjpark@amazon.de>
---
drivers/xen/xenbus/xenbus_probe.c | 8 +++++++-
drivers/xen/xenbus/xenbus_probe_backend.c | 10 ++++++++--
include/xen/xenbus.h | 1 +
3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index 378486b79f96..66975da4f3b6 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -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);
diff --git a/drivers/xen/xenbus/xenbus_probe_backend.c b/drivers/xen/xenbus/xenbus_probe_backend.c
index 3b5cb7a5a7e4..791f6fe01e91 100644
--- a/drivers/xen/xenbus/xenbus_probe_backend.c
+++ b/drivers/xen/xenbus/xenbus_probe_backend.c
@@ -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;
}

diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h
index 980952ea452b..89a889585ba0 100644
--- a/include/xen/xenbus.h
+++ b/include/xen/xenbus.h
@@ -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)
--
2.17.1