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 13:03:42 +0800 |
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On Tue, 2014-04-22 at 16:44 -0400, Tejun Heo wrote: > Hello, > > On Tue, Apr 22, 2014 at 11:34:39AM +0800, Li Zhong wrote: > > > 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. > > I'm confused about the overall locking scheme. What's the role of > device_hotplug_lock? Is that solely to prevent the sysfs deadlock > issue? Or does it serve other synchronization purposes depending on > the specific subsystem? If the former, the lock no longer needs to > exist. The only thing necessary would be synchronization between > device_del() deleting the sysfs file and the unbreak helper invoking > device-specific callback. If the latter, we probably should change > that. Sharing hotplug lock across multiple subsystems through driver > core sounds like a pretty bad idea.
I think it's the latter. I think device_{on|off}line is better to be done in some sort of lock which prevents the device from being removed, including some preparation work that needs be done before device_del().
Thanks, Zhong
> > Thanks. >
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