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

[<sjpark@xxxxxxxxxx>]

From: SeongJae Park <sjpark@xxxxxxxxx>

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@xxxxxxxx>
Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx>
---
 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


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