[PATCH] Disable CPU hotplug during suspend

The current suspend code has to be run on one CPU, so we use the CPU
hotplug to take the non-boot CPUs offline on SMP machines.  However, we
should also make sure that these CPUs will not be enabled by someone else
after we have disabled them.

The functions disable_nonboot_cpus() and enable_nonboot_cpus() are moved to
kernel/cpu.c, because they now refer to some stuff in there that should
better be static.  Also it's better if disable_nonboot_cpus() returns an
error instead of panicking if something goes wrong, and
enable_nonboot_cpus() has no reason to panic(), because the CPUs may have
been enabled by the userland before it tries to take them online.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 118 insertions, 20 deletions

diff --git a/kernel/cpu.c b/kernel/cpu.c
index f230f9ae01c2..32c96628463e 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -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 +179,32 @@ 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)
+/* Requires cpu_add_remove_lock to be held */
+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 +229,95 @@ 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