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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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