Messages in this thread | | | Subject | Re: [RFC PATCH v5 2/2] Use kernfs_break_active_protection() for device online store callbacks | From | Li Zhong <> | Date | Wed, 23 Apr 2014 09:50:32 +0800 |
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On Tue, 2014-04-22 at 12:11 +0200, Rafael J. Wysocki wrote: > 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.
This is talking about the lock required in the other process, the device removing process, e.g. that in remove_memory() below. So I guess no lockdep assertions needed here. Or I misunderstand your point?
> > > > 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.
OK, I see. I think I'll just add lockdep assertions, and keep the comments there.
Thanks, Zhong
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