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    SubjectRe: [RFC PATCH v5 2/2] Use kernfs_break_active_protection() for device online store callbacks
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    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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