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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
