On Tuesday 27 January 2009 08:47:29 Ingo Molnar wrote: > > * Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > > > But "[PATCH 1/3] work_on_cpu: dont try to get_online_cpus() in > > work_on_cpu." removes get_online_cpus/put_online_cpus, this means the > > work can run on the wrong CPU anyway. Or work_on_cpu() can hang forever > > if CPU has already gone away before queue_work_on(). > > > > Confused. > > The idea was to require work_on_cpu() users to be CPU hotplug-safe. But > ... Rusty pointed it out in the past that this might be fragile, and we > could put back the get_online_cpus()/put_online_cpus() calls. Old code used to do: tmp = current->cpus_allowed; set_cpus_allowed(current, cpumask_of_cpu(cpu)); function(arg); set_cpus_allowed(current, tmp); We replaced it with: work_on_cpu(cpu, function, arg); I thought I'd be clever and reliably check that the cpu they asked for was online inside work_on_cpu. Leading to locking problems. But if they didn't previously ensure cpu hotplug didn't happen, they were buggy already, so I took out the check and hence the hotplug lock. So we're no *worse* than we were before, but yes, an audit would probably lead to fixes. Hope that clarifies? Rusty. -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
