path: root/arch
diff options
authorHeiko Carstens <heiko.carstens@de.ibm.com>2012-07-13 15:45:33 +0200
committerMartin Schwidefsky <schwidefsky@de.ibm.com>2012-07-17 10:34:27 +0200
commit0008204ffe85d23382d6fd0f971f3f0fbe70bae2 (patch)
tree0efd42411102e2b75a7707b959be0933ba70383f /arch
parent8738e07d5c9b5b02f113c7e0ba67f0d8d6a5b23c (diff)
s390/idle: fix sequence handling vs cpu hotplug
The s390 idle accounting code uses a sequence counter which gets used when the per cpu idle statistics get updated and read. One assumption on read access is that only when the sequence counter is even and did not change while reading all values the result is valid. On cpu hotplug however the per cpu data structure gets initialized via a cpu hotplug notifier on CPU_ONLINE. CPU_ONLINE however is too late, since the onlined cpu is already running and might access the per cpu data. Worst case is that the data structure gets initialized while an idle thread is updating its idle statistics. This will result in an uneven sequence counter after an update. As a result user space tools like top, which access /proc/stat in order to get idle stats, will busy loop waiting for the sequence counter to become even again, which will never happen until the queried cpu will update its idle statistics again. And even then the sequence counter will only have an even value for a couple of cpu cycles. Fix this by moving the initialization of the per cpu idle statistics to cpu_init(). I prefer that solution in favor of changing the notifier to CPU_UP_PREPARE, which would be a different solution to the problem. Cc: stable@vger.kernel.org Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Diffstat (limited to 'arch')
2 files changed, 2 insertions, 3 deletions
diff --git a/arch/s390/kernel/processor.c b/arch/s390/kernel/processor.c
index 6e0073e43f54..07c7bf47d618 100644
--- a/arch/s390/kernel/processor.c
+++ b/arch/s390/kernel/processor.c
@@ -26,12 +26,14 @@ static DEFINE_PER_CPU(struct cpuid, cpu_id);
void __cpuinit cpu_init(void)
struct cpuid *id = &per_cpu(cpu_id, smp_processor_id());
+ struct s390_idle_data *idle = &__get_cpu_var(s390_idle);
current->active_mm = &init_mm;
enter_lazy_tlb(&init_mm, current);
+ memset(idle, 0, sizeof(*idle));
diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index dc602a61233f..22257f241d07 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -959,14 +959,11 @@ static int __cpuinit smp_cpu_notify(struct notifier_block *self,
unsigned int cpu = (unsigned int)(long)hcpu;
struct cpu *c = &pcpu_devices[cpu].cpu;
struct device *s = &c->dev;
- struct s390_idle_data *idle;
int err = 0;
switch (action) {
- idle = &per_cpu(s390_idle, cpu);
- memset(idle, 0, sizeof(struct s390_idle_data));
err = sysfs_create_group(&s->kobj, &cpu_online_attr_group);
case CPU_DEAD: