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SubjectRe: [PATCH v11 2/6] xenbus/backend: Protect xenbus callback with lock
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On 17.12.19 17:07, SeongJae Park wrote:
> From: SeongJae Park <sjpark@amazon.de>
>
> '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@amazon.de>
> ---
> 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

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