Re: [PATCH -mm][resend] Disable CPU hotplug during suspend

Rafael J. Wysocki
2006-07-28T21:24:07Z

On Friday 28 July 2006 21:15, Rafael J. Wysocki wrote:
> Hi Nathan,
>
> On Friday 28 July 2006 20:20, Nathan Lynch wrote:
> > Hi Rafael-
> >
]--snip--[
> I'm not quite sure if we can finish with CPU0 offline. Perhaps it's better to
> check if CPU0 is online and bring it up if not and then continue or return
> an error if that fails?

I've tried to implement this idea in the appended patch (I'm omitting the
changes outside of kernel/cpu.c as they are not relevant here).

Please have a look.

Rafael

--- linux-2.6.18-rc2-mm1.orig/kernel/cpu.c 2006-07-28 21:03:21.000000000 +0200
+++ linux-2.6.18-rc2-mm1/kernel/cpu.c 2006-07-28 22:59:03.000000000 +0200
@@ -21,6 +21,11 @@ static DEFINE_MUTEX(cpu_bitmask_lock);

static __cpuinitdata BLOCKING_NOTIFIER_HEAD(cpu_chain);

+/* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
+ * Should always be manipulated under cpu_add_remove_lock
+ */
+static int cpu_hotplug_disabled;
+
#ifdef CONFIG_HOTPLUG_CPU

/* Crappy recursive lock-takers in cpufreq! Complain loudly about idiots */
@@ -108,30 +113,25 @@ static int take_cpu_down(void *unused)
return 0;
}

-int cpu_down(unsigned int cpu)
+/* Requires cpu_add_remove_lock to be held */
+static int _cpu_down(unsigned int cpu)
{
int err;
struct task_struct *p;
cpumask_t old_allowed, tmp;

- mutex_lock(&cpu_add_remove_lock);
- if (num_online_cpus() == 1) {
- err = -EBUSY;
- goto out;
- }
+ if (num_online_cpus() == 1)
+ return -EBUSY;

- if (!cpu_online(cpu)) {
- err = -EINVAL;
- goto out;
- }
+ if (!cpu_online(cpu))
+ return -EINVAL;

err = blocking_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,
(void *)(long)cpu);
if (err == NOTIFY_BAD) {
printk("%s: attempt to take down CPU %u failed\n",
__FUNCTION__, cpu);
- err = -EINVAL;
- goto out;
+ return -EINVAL;
}

/* Ensure that we are not runnable on dying cpu */
@@ -179,22 +179,31 @@ out_thread:
err = kthread_stop(p);
out_allowed:
set_cpus_allowed(current, old_allowed);
-out:
+ return err;
+}
+
+int cpu_down(unsigned int cpu)
+{
+ int err = 0;
+
+ mutex_lock(&cpu_add_remove_lock);
+ if (cpu_hotplug_disabled)
+ err = -EBUSY;
+ else
+ err = _cpu_down(cpu);
+
mutex_unlock(&cpu_add_remove_lock);
return err;
}
#endif /*CONFIG_HOTPLUG_CPU*/

-int __devinit cpu_up(unsigned int cpu)
+static int __devinit _cpu_up(unsigned int cpu)
{
int ret;
void *hcpu = (void *)(long)cpu;

- mutex_lock(&cpu_add_remove_lock);
- if (cpu_online(cpu) || !cpu_present(cpu)) {
- ret = -EINVAL;
- goto out;
- }
+ if (cpu_online(cpu) || !cpu_present(cpu))
+ return -EINVAL;

ret = blocking_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
if (ret == NOTIFY_BAD) {
@@ -219,7 +228,95 @@ out_notify:
if (ret != 0)
blocking_notifier_call_chain(&cpu_chain,
CPU_UP_CANCELED, hcpu);
+
+ return ret;
+}
+
+int __devinit cpu_up(unsigned int cpu)
+{
+ int err = 0;
+
+ mutex_lock(&cpu_add_remove_lock);
+ if (cpu_hotplug_disabled)
+ err = -EBUSY;
+ else
+ err = _cpu_up(cpu);
+
+ mutex_unlock(&cpu_add_remove_lock);
+ return err;
+}
+
+#ifdef CONFIG_SUSPEND_SMP
+static cpumask_t frozen_cpus;
+
+int disable_nonboot_cpus(void)
+{
+ int cpu, first_cpu, error;
+
+ mutex_lock(&cpu_add_remove_lock);
+ first_cpu = first_cpu(cpu_present_map);
+ if (!cpu_online(first_cpu)) {
+ error = _cpu_up(first_cpu);
+ if (error) {
+ printk(KERN_ERR "Could not bring CPU%d up.\n",
+ first_cpu);
+ goto out;
+ }
+ }
+ error = set_cpus_allowed(current, cpumask_of_cpu(first_cpu));
+ if (error) {
+ printk(KERN_ERR "Could not run on CPU%d\n", first_cpu);
+ goto out;
+ }
+ /* We take down all of the non-boot CPUs in one shot to avoid races
+ * with the userspace trying to use the CPU hotplug at the same time
+ */
+ cpus_clear(frozen_cpus);
+ printk("Disabling non-boot CPUs ...\n");
+ for_each_online_cpu(cpu) {
+ if (cpu == first_cpu)
+ continue;
+ error = _cpu_down(cpu);
+ if (!error) {
+ cpu_set(cpu, frozen_cpus);
+ printk("CPU%d is down\n", cpu);
+ } else {
+ printk(KERN_ERR "Error taking CPU%d down: %d\n",
+ cpu, error);
+ break;
+ }
+ }
+ if (!error) {
+ BUG_ON(num_online_cpus() > 1);
+ /* Make sure the CPUs won't be enabled by someone else */
+ cpu_hotplug_disabled = 1;
+ } else {
+ printk(KERN_ERR "Non-boot CPUs are not disabled");
+ }
out:
mutex_unlock(&cpu_add_remove_lock);
- return ret;
+ return error;
+}
+
+void enable_nonboot_cpus(void)
+{
+ int cpu, error;
+
+ /* Allow everyone to use the CPU hotplug again */
+ mutex_lock(&cpu_add_remove_lock);
+ cpu_hotplug_disabled = 0;
+ mutex_unlock(&cpu_add_remove_lock);
+
+ printk("Enabling non-boot CPUs ...\n");
+ for_each_cpu_mask(cpu, frozen_cpus) {
+ error = cpu_up(cpu);
+ if (!error) {
+ printk("CPU%d is up\n", cpu);
+ continue;
+ }
+ printk(KERN_WARNING "Error taking CPU%d up: %d\n",
+ cpu, error);
+ }
+ cpus_clear(frozen_cpus);
}
+#endif