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Koen Kooi
6203cbca5c
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net> Signed-off-by: Denys Dmytriyenko <denys@ti.com>
81 lines
3.0 KiB
Diff
81 lines
3.0 KiB
Diff
From 9385ba7e09e3360516f2b3c78c7d8f233dd1119f Mon Sep 17 00:00:00 2001
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From: Heiko Carstens <heiko.carstens@de.ibm.com>
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Date: Fri, 13 Jul 2012 15:45:33 +0200
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Subject: [PATCH 45/73] s390/idle: fix sequence handling vs cpu hotplug
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commit 0008204ffe85d23382d6fd0f971f3f0fbe70bae2 upstream.
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The s390 idle accounting code uses a sequence counter which gets used
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when the per cpu idle statistics get updated and read.
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One assumption on read access is that only when the sequence counter is
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even and did not change while reading all values the result is valid.
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On cpu hotplug however the per cpu data structure gets initialized via
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a cpu hotplug notifier on CPU_ONLINE.
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CPU_ONLINE however is too late, since the onlined cpu is already running
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and might access the per cpu data. Worst case is that the data structure
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gets initialized while an idle thread is updating its idle statistics.
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This will result in an uneven sequence counter after an update.
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As a result user space tools like top, which access /proc/stat in order
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to get idle stats, will busy loop waiting for the sequence counter to
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become even again, which will never happen until the queried cpu will
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update its idle statistics again. And even then the sequence counter
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will only have an even value for a couple of cpu cycles.
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Fix this by moving the initialization of the per cpu idle statistics
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to cpu_init(). I prefer that solution in favor of changing the
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notifier to CPU_UP_PREPARE, which would be a different solution to
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the problem.
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Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
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Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
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[bwh: Backported to 3.2: adjust context]
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Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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---
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arch/s390/kernel/processor.c | 2 ++
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arch/s390/kernel/smp.c | 3 ---
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2 files changed, 2 insertions(+), 3 deletions(-)
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diff --git a/arch/s390/kernel/processor.c b/arch/s390/kernel/processor.c
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index 6e0073e..07c7bf4 100644
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--- a/arch/s390/kernel/processor.c
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+++ b/arch/s390/kernel/processor.c
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@@ -26,12 +26,14 @@ static DEFINE_PER_CPU(struct cpuid, cpu_id);
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void __cpuinit cpu_init(void)
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{
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struct cpuid *id = &per_cpu(cpu_id, smp_processor_id());
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+ struct s390_idle_data *idle = &__get_cpu_var(s390_idle);
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get_cpu_id(id);
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atomic_inc(&init_mm.mm_count);
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current->active_mm = &init_mm;
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BUG_ON(current->mm);
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enter_lazy_tlb(&init_mm, current);
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+ memset(idle, 0, sizeof(*idle));
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}
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/*
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diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
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index 3ea8728..1df64a8 100644
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--- a/arch/s390/kernel/smp.c
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+++ b/arch/s390/kernel/smp.c
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@@ -1020,14 +1020,11 @@ static int __cpuinit smp_cpu_notify(struct notifier_block *self,
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unsigned int cpu = (unsigned int)(long)hcpu;
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struct cpu *c = &per_cpu(cpu_devices, cpu);
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struct sys_device *s = &c->sysdev;
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- struct s390_idle_data *idle;
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int err = 0;
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switch (action) {
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case CPU_ONLINE:
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case CPU_ONLINE_FROZEN:
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- idle = &per_cpu(s390_idle, cpu);
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- memset(idle, 0, sizeof(struct s390_idle_data));
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err = sysfs_create_group(&s->kobj, &cpu_online_attr_group);
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break;
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case CPU_DEAD:
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--
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1.7.7.6
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