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sched, cpu hotplug: fix set_cpus_allowed() use in hotplug callbacks
Mark Langsdorf reported: > One of my co-workers noticed that the powernow-k8 > driver no longer restarts when a CPU core is > hot-disabled and then hot-enabled on AMD quad-core > systems. > > The following comands work fine on 2.6.26 and fail > on 2.6.27-rc1: > > echo 0 > /sys/devices/system/cpu/cpu3/online > echo 1 > /sys/devices/system/cpu/cpu3/online > find /sys -name cpufreq > > For 2.6.26, the find will return a cpufreq > directory for each processor. In 2.6.27-rc1, > the cpu3 directory is missing. > > After digging through the code, the following > logic is failing when the core is hot-enabled > at runtime. The code works during the boot > sequence. > > cpumask_t = current->cpus_allowed; > set_cpus_allowed_ptr(current, &cpumask_of_cpu(cpu)); > if (smp_processor_id() != cpu) > return -ENODEV; So set the CPU active before calling the CPU_ONLINE notifier chain, there are a handful of notifiers that use set_cpus_allowed(). This fix also solves the problem with x86-microcode. I've sent alternative patches for microcode, but as this "rely on set_cpus_allowed_ptr() being workable in cpu-hotplug(CPU_ONLINE, ...)" assumption seems to be more broad than what we thought, perhaps this fix should be applied. With this patch we define that by the moment CPU_ONLINE is being sent, a 'cpu' is online and ready for tasks to be migrated onto it. Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com> Reported-by: Mark Langsdorf <mark.langsdorf@amd.com> Tested-by: Mark Langsdorf <mark.langsdorf@amd.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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@ -349,6 +349,8 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
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goto out_notify;
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BUG_ON(!cpu_online(cpu));
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cpu_set(cpu, cpu_active_map);
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/* Now call notifier in preparation. */
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raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
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@ -383,9 +385,6 @@ int __cpuinit cpu_up(unsigned int cpu)
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err = _cpu_up(cpu, 0);
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if (cpu_online(cpu))
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cpu_set(cpu, cpu_active_map);
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out:
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cpu_maps_update_done();
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return err;
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