Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [RFC PATCH v5 2/2] Use kernfs_break_active_protection() for device online store callbacks | Date | Tue, 22 Apr 2014 12:11:53 +0200 |
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On Tuesday, April 22, 2014 11:34:39 AM 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. > > > > > > { > > ... > > > + /* > > > + * 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.
Well, I haven't been following this closely (I was travelling, sorry), but there certainly are devices without online/offline. That currently is only present for CPUs, memory blocks and ACPI containers (if I remember correctly).
> > 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. ... > ?
Lockdep assertions would be better than this in my opinion.
> > 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.
No, please don't remove it. It is there to explain where the locking requirement comes from.
-- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.
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