Messages in this thread | | | Subject | Re: [PATCH v11 2/6] xenbus/backend: Protect xenbus callback with lock | From | Jürgen Groß <> | Date | Tue, 17 Dec 2019 17:13:42 +0100 |
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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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