Messages in this thread | | | Date | Wed, 05 Dec 2012 18:11:51 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [RFC PATCH 02/10] smp, cpu hotplug: Fix smp_call_function_*() to prevent CPU offline properly |
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On 12/05/2012 03:47 AM, Andrew Morton wrote: > On Tue, 04 Dec 2012 14:24:28 +0530 > "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com> wrote: > >> From: Michael Wang <wangyun@linux.vnet.ibm.com> >> >> With stop_machine() gone from the CPU offline path, we can't depend on >> preempt_disable() to prevent CPUs from going offline from under us. >> >> Use the get/put_online_cpus_stable_atomic() APIs to prevent CPUs from going >> offline, while invoking from atomic context. >> >> ... >> >> */ >> - this_cpu = get_cpu(); >> + get_online_cpus_stable_atomic(); >> + this_cpu = smp_processor_id(); > > I wonder if get_online_cpus_stable_atomic() should return the local CPU > ID. Just as a little convenience thing. Time will tell. >
With the new version which doesn't use extra cpumasks, we won't have to bother about this..
>> /* >> * Can deadlock when called with interrupts disabled. >> >> ... >> >> @@ -380,15 +383,15 @@ int smp_call_function_any(const struct cpumask *mask, >> nodemask = cpumask_of_node(cpu_to_node(cpu)); >> for (cpu = cpumask_first_and(nodemask, mask); cpu < nr_cpu_ids; >> cpu = cpumask_next_and(cpu, nodemask, mask)) { >> - if (cpu_online(cpu)) >> + if (cpu_online_stable(cpu)) >> goto call; >> } >> >> /* Any online will do: smp_call_function_single handles nr_cpu_ids. */ >> - cpu = cpumask_any_and(mask, cpu_online_mask); >> + cpu = cpumask_any_and(mask, cpu_online_stable_mask); >> call: >> ret = smp_call_function_single(cpu, func, info, wait); >> - put_cpu(); >> + put_online_cpus_stable_atomic(); >> return ret; >> } >> EXPORT_SYMBOL_GPL(smp_call_function_any); > > So smp_call_function_any() has no synchronization against CPUs coming > online. Hence callers of smp_call_function_any() are responsible for > ensuring that CPUs which are concurrently coming online will adopt the > required state? >
Yes.
> I guess that has always been the case... >
Right.
Regards, Srivatsa S. Bhat
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