viOn Tue, 2014-04-22 at 11:34 +0800, Li Zhong wrote:
> On Mon, 2014-04-21 at 18:46 -0400, Tejun Heo wrote:
> > Hello,
> >
> > On Mon, Apr 21, 2014 at 05:23:50PM +0800, Li Zhong wrote:
> >
> > Proper /** function comment would be nice.
>
> Ok, will try to write some in next version.
>
> >
> > > +struct kernfs_node *lock_device_hotplug_sysfs(struct device *dev,
> > > + struct device_attribute *attr)
> >
> > I can see why you did this but let's please not require the user of
> > this function to see how the thing is working internally. Let's
> > return int and keep track of (or look up again) the kernfs_node
> > internally.
>
> Ok, it also makes the prototype of lock and unlock look more consistent
> and comfortable.
When trying to do an new version of the patch, I find that if the device
is really removed, then we couldn't look up using the parent, and
attribute name again in unlock. So I guess maybe I could add one more
argument, e.g. kn_out,:q to track this kernfs node.
Code will be posted soon for your review.
Thanks, Zhong
>
> >
> > > {
> > ...
> > > + /*
> > > + * We assume device_hotplug_lock must be acquired before removing
> >
> > Is this assumption true? If so, can we add lockdep assertions in
> > places to verify and enforce this? If not, aren't we just feeling
> > good when the reality is broken?
>
> It seems not true ... I think there are devices that don't have the
> online/offline concept, we just need to add it, remove it, like ethernet
> cards.
>
> Maybe we could change the comments above, like:
> /* We assume device_hotplug_lock must be acquired before
> * removing devices, which have online/offline sysfs knob,
> * and some locks are needed to serialize the online/offline
> * callbacks and device removing. ...
> ?
>
> And we could add lockdep assertions in cpu and memory related code? e.g.
> remove_memory(), unregister_cpu()
>
> Currently, remove_memory() has comments for the function:
>
> * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
> * and online/offline operations before this call, as required by
> * try_offline_node().
> */
>
> maybe it could be removed with the lockdep assertion.
>
> > ...
> >
> > Function comment please.
>
> OK.
>
> Thanks, Zhong
>
> > > +void unlock_device_hotplug_sysfs(struct device *dev,
> > > + struct kernfs_node *kn)
> > > +{
> > > + unlock_device_hotplug();
> > > + kernfs_unbreak_active_protection(kn);
> > > + put_device(dev);
> > > + kernfs_put(kn);
> > > }
> >
> > Thanks.
> >
>
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