From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
commit 8cdddd182bd7befae6af49c5fd612893f55d6ccb upstream.
Commit 496121c02127 ("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: 496121c02127 ("ACPI: processor: idle: Allow probing on platforms with one ACPI C-state")
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Cc: 5.10+ <stable@xxxxxxxxxxxxxxx> # 5.10+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/smp.h | 1 +
arch/x86/kernel/smpboot.c | 2 +-
drivers/acpi/processor_idle.c | 7 +++++++
3 files changed, 9 insertions(+), 1 deletion(-)
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -132,6 +132,7 @@ void native_play_dead(void);
void play_dead_common(void);
void wbinvd_on_cpu(int cpu);
int wbinvd_on_all_cpus(void);
+bool wakeup_cpu0(void);
void native_smp_send_reschedule(int cpu);
void native_send_call_func_ipi(const struct cpumask *mask);
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1655,7 +1655,7 @@ void play_dead_common(void)
local_irq_disable();
}
-static bool wakeup_cpu0(void)
+bool wakeup_cpu0(void)
{
if (smp_processor_id() == 0 && enable_start_cpu0)
return true;
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -29,6 +29,7 @@
*/
#ifdef CONFIG_X86
#include <asm/apic.h>
+#include <asm/cpu.h>
#endif
#define ACPI_PROCESSOR_CLASS "processor"
@@ -542,6 +543,12 @@ static int acpi_idle_play_dead(struct cp
wait_for_freeze();
} else
return -ENODEV;
+
+#if defined(CONFIG_X86) && defined(CONFIG_HOTPLUG_CPU)
+ /* If NMI wants to wake up CPU0, start CPU0. */
+ if (wakeup_cpu0())
+ start_cpu0();
+#endif
}
/* Never reached */
