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ACPI: processor: Fix CPU0 wakeup in acpi_idle_play_dead()
Commit496121c021
("ACPI: processor: idle: Allow probing on platforms with one ACPI C-state") broke CPU0 hotplug on certain systems, e.g. I'm observing the following on AWS Nitro (e.g r5b.xlarge but other instance types are affected as well): # echo 0 > /sys/devices/system/cpu/cpu0/online # echo 1 > /sys/devices/system/cpu/cpu0/online <10 seconds delay> -bash: echo: write error: Input/output error In fact, the above mentioned commit only revealed the problem and did not introduce it. On x86, to wakeup CPU an NMI is being used and hlt_play_dead()/mwait_play_dead() loops are prepared to handle it: /* * If NMI wants to wake up CPU0, start CPU0. */ if (wakeup_cpu0()) start_cpu0(); cpuidle_play_dead() -> acpi_idle_play_dead() (which is now being called on systems where it wasn't called before the above mentioned commit) serves the same purpose but it doesn't have a path for CPU0. What happens now on wakeup is: - NMI is sent to CPU0 - wakeup_cpu0_nmi() works as expected - we get back to while (1) loop in acpi_idle_play_dead() - safe_halt() puts CPU0 to sleep again. The straightforward/minimal fix is add the special handling for CPU0 on x86 and that's what the patch is doing. Fixes:496121c021
("ACPI: processor: idle: Allow probing on platforms with one ACPI C-state") Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Cc: 5.10+ <stable@vger.kernel.org> # 5.10+ Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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3 changed files with 9 additions and 1 deletions
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@ -132,6 +132,7 @@ void native_play_dead(void);
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void play_dead_common(void);
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void wbinvd_on_cpu(int cpu);
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int wbinvd_on_all_cpus(void);
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bool wakeup_cpu0(void);
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void native_smp_send_reschedule(int cpu);
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void native_send_call_func_ipi(const struct cpumask *mask);
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@ -1659,7 +1659,7 @@ void play_dead_common(void)
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local_irq_disable();
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}
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static bool wakeup_cpu0(void)
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bool wakeup_cpu0(void)
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{
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if (smp_processor_id() == 0 && enable_start_cpu0)
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return true;
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@ -29,6 +29,7 @@
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*/
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#ifdef CONFIG_X86
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#include <asm/apic.h>
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#include <asm/cpu.h>
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#endif
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#define _COMPONENT ACPI_PROCESSOR_COMPONENT
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@ -541,6 +542,12 @@ static int acpi_idle_play_dead(struct cpuidle_device *dev, int index)
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wait_for_freeze();
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} else
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return -ENODEV;
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#if defined(CONFIG_X86) && defined(CONFIG_HOTPLUG_CPU)
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/* If NMI wants to wake up CPU0, start CPU0. */
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if (wakeup_cpu0())
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start_cpu0();
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#endif
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}
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/* Never reached */
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