On 17.12.19 17:07, SeongJae Park wrote:
From: SeongJae Park <sjpark@xxxxxxxxx>
'reclaim_memory' callback can race with a driver code as this callback
will be called from any memory pressure detected context. To deal with
the case, this commit adds a spinlock in the 'xenbus_device'. Whenever
'reclaim_memory' callback is called, the lock of the device which passed
to the callback as its argument is locked. Thus, drivers registering
their 'reclaim_memory' callback should protect the data that might race
with the callback with the lock by themselves.
Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx>
---
drivers/xen/xenbus/xenbus_probe.c | 1 +
drivers/xen/xenbus/xenbus_probe_backend.c | 10 ++++++++--
include/xen/xenbus.h | 2 ++
3 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index 5b471889d723..b86393f172e6 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -472,6 +472,7 @@ 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 7e78ebef7c54..516aa64b9967 100644
--- a/drivers/xen/xenbus/xenbus_probe_backend.c
+++ b/drivers/xen/xenbus/xenbus_probe_backend.c
@@ -251,12 +251,18 @@ 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;
+ unsigned long flags;
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);
+ spin_trylock_irqsave(&xdev->reclaim_lock, flags);
You need spin_lock_irqsave() here. Or maybe spin_lock() would be fine,
too? I can't see a reason why you'd want to disable irqs here.
+ drv->reclaim_memory(xdev);
+ spin_unlock_irqrestore(&xdev->reclaim_lock, flags);
+ }
return 0;
}
diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h
index c861cfb6f720..d9468313061d 100644
--- a/include/xen/xenbus.h
+++ b/include/xen/xenbus.h
@@ -76,6 +76,8 @@ struct xenbus_device {
enum xenbus_state state;
struct completion down;
struct work_struct work;
+ /* 'reclaim_memory' callback is called while this lock is acquired */
+ spinlock_t reclaim_lock;
};
static inline struct xenbus_device *to_xenbus_device(struct device *dev)
Juergen
