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authorVitaly Kuznetsov <vkuznets@redhat.com>2021-03-24 18:22:19 +0300
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2021-04-01 14:37:55 +0300
commit8cdddd182bd7befae6af49c5fd612893f55d6ccb (patch)
treed082d5e17f703d2d18dcd6b729e734b592e47849 /arch
parenta5e13c6df0e41702d2b2c77c8ad41677ebb065b3 (diff)
downloadlinux-8cdddd182bd7befae6af49c5fd612893f55d6ccb.tar.xz
ACPI: processor: Fix CPU0 wakeup in acpi_idle_play_dead()
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@redhat.com> Cc: 5.10+ <stable@vger.kernel.org> # 5.10+ Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/include/asm/smp.h1
-rw-r--r--arch/x86/kernel/smpboot.c2
2 files changed, 2 insertions, 1 deletions
diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index c0538f82c9a2..57ef2094af93 100644
--- 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);
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 02813a7f3a7c..f877150a91da 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1659,7 +1659,7 @@ 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;