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    Subject[PATCH v13 2/5] xenbus/backend: Protect xenbus callback with lock
    Date
    From: SeongJae Park <sjpark@amazon.de>

    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.

    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 5b471889d723..9ed556ba4fd4 100644
    --- a/drivers/xen/xenbus/xenbus_probe.c
    +++ b/drivers/xen/xenbus/xenbus_probe.c
    @@ -232,7 +232,9 @@ int xenbus_dev_probe(struct device *_dev)
    return err;
    }

    + spin_lock(&dev->reclaim_lock);
    err = drv->probe(dev, id);
    + spin_unlock(&dev->reclaim_lock);
    if (err)
    goto fail;

    @@ -260,8 +262,11 @@ 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);
    + }

    free_otherend_details(dev);

    @@ -472,6 +477,7 @@ 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..bc61372e00a1 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;

    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 c861cfb6f720..45cd61cb6e86 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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