Messages in this thread | | | Date | Thu, 06 Dec 2012 00:31:14 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [RFC PATCH v2 02/10] CPU hotplug: Provide APIs for "full" atomic readers to prevent CPU offline |
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Replaying what Tejun wrote:
On 12/06/2012 12:13 AM, Srivatsa S. Bhat wrote: > Some of the atomic hotplug readers cannot tolerate CPUs going offline while > they are in their critical section. That is, they can't get away with just > synchronizing with the updates to the cpu_online_mask; they really need to > synchronize with the entire CPU tear-down sequence, because they are very > much involved in the hotplug related code paths. > > Such "full" atomic hotplug readers need a way to *actually* and *truly* > prevent CPUs from going offline while they are active. >
I don't think this is a good idea. You really should just need get/put_online_cpus() and get/put_online_cpus_atomic(). The former the same as they are. The latter replacing what preempt_disable/enable() was protecting. Let's please not go overboard unless we know they're necessary. I strongly suspect that breaking up reader side from preempt_disable and making writer side a bit lighter should be enough. Conceptually, it really should be a simple conversion - convert preempt_disable/enable() pairs protecting CPU on/offlining w/ get/put_cpu_online_atomic() and wrap the stop_machine() section with the matching write lock.
Thanks.
-- tejun
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