Messages in this thread | | | Date | Thu, 23 Jan 2014 11:06:29 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: Deadlock between cpu_hotplug_begin and cpu_add_remove_lock |
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On 01/23/2014 07:59 AM, Rusty Russell wrote: > "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com> writes: >> On 01/22/2014 02:00 PM, Srivatsa S. Bhat wrote: >>> Hi Paul, > > I find an old patch for register_allcpu_notifier(), but the "bool > replay_history" should be eliminated (always true): it's too weird. >
Sorry, I didn't get this part. Why do you say that replay_history will always be true?
replay_history will be set to true whenever the caller wants to get notified of CPU_UP_PREPARE and CPU_ONLINE notifications for the already online CPUs, or wants to run a custom setup-routine of its own. And it will be false whenever the caller simply wants to just register the callback.
Note that passing NULL for the setup-routine, by itself isn't enough to make a decision. NULL + replay_history == True will invoke the normal CPU_UP_PREPARE/CPU_ONLINE notifiers for the already online CPUs before registering the callback. NULL + replay_history == False will just register the callback and do nothing else.
> Then we should get rid of register_cpu_notifier, or at least hide it. >
Why? Isn't it easier to use (since you don't have to pass 2 additional parameters)? I see register_allcpu_notifier (or whatever better name we can give it), as an API for special cases where there is something more to be done than just registering the callback. And register_cpu_notifier will continue to be the API for the regular case when the caller wants to just register the callback. This latter case is the majority in the kernel. So I don't think eliminating the regular API would be a good idea.
By the way, I'm still tempted to try out the simpler-looking alternative idea of exporting cpu_maps_update_begin() and cpu_maps_update_done() and then mandating that the callers do:
cpu_maps_update_begin(); for_each_online_cpu(cpu) { ... }
__register_cpu_notifier(); // this doesn't take the add_remove_lock cpu_maps_update_done();
I'm working on a patchset that does this and performs a tree-wide conversion. Please let me know if you have any objections to exporting cpu_maps_update_begin/done() in this manner.
I thought I'd give this solution a try first, before going to the much fancier register_allcpu_notifier() method.
Regards, Srivatsa S. Bhat
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