1 files changed, 56 insertions, 1 deletions

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 2060c6e57027..a4eb5227a19e 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -10,13 +10,18 @@
 #include <linux/sched.h>
 #include <linux/unistd.h>
 #include <linux/cpu.h>
+#include <linux/oom.h>
+#include <linux/rcupdate.h>
 #include <linux/export.h>
+#include <linux/bug.h>
 #include <linux/kthread.h>
 #include <linux/stop_machine.h>
 #include <linux/mutex.h>
 #include <linux/gfp.h>
 #include <linux/suspend.h>
 
+#include "smpboot.h"
+
 #ifdef CONFIG_SMP
 /* Serializes the updates to cpu_online_mask, cpu_present_mask */
 static DEFINE_MUTEX(cpu_add_remove_lock);
@@ -171,6 +176,47 @@ void __ref unregister_cpu_notifier(struct notifier_block *nb)
 }
 EXPORT_SYMBOL(unregister_cpu_notifier);
 
+/**
+ * clear_tasks_mm_cpumask - Safely clear tasks' mm_cpumask for a CPU
+ * @cpu: a CPU id
+ *
+ * This function walks all processes, finds a valid mm struct for each one and
+ * then clears a corresponding bit in mm's cpumask.  While this all sounds
+ * trivial, there are various non-obvious corner cases, which this function
+ * tries to solve in a safe manner.
+ *
+ * Also note that the function uses a somewhat relaxed locking scheme, so it may
+ * be called only for an already offlined CPU.
+ */
+void clear_tasks_mm_cpumask(int cpu)
+{
+        struct task_struct *p;
+
+        /*
+         * This function is called after the cpu is taken down and marked
+         * offline, so its not like new tasks will ever get this cpu set in
+         * their mm mask. -- Peter Zijlstra
+         * Thus, we may use rcu_read_lock() here, instead of grabbing
+         * full-fledged tasklist_lock.
+         */
+        WARN_ON(cpu_online(cpu));
+        rcu_read_lock();
+        for_each_process(p) {
+                struct task_struct *t;
+
+                /*
+                 * Main thread might exit, but other threads may still have
+                 * a valid mm. Find one.
+                 */
+                t = find_lock_task_mm(p);
+                if (!t)
+                        continue;
+                cpumask_clear_cpu(cpu, mm_cpumask(t->mm));
+                task_unlock(t);
+        }
+        rcu_read_unlock();
+}
+
 static inline void check_for_tasks(int cpu)
 {
         struct task_struct *p;
@@ -295,11 +341,19 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
         int ret, nr_calls = 0;
         void *hcpu = (void *)(long)cpu;
         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
+        struct task_struct *idle;
 
         if (cpu_online(cpu) || !cpu_present(cpu))
                 return -EINVAL;
 
         cpu_hotplug_begin();
+
+        idle = idle_thread_get(cpu);
+        if (IS_ERR(idle)) {
+                ret = PTR_ERR(idle);
+                goto out;
+        }
+
         ret = __cpu_notify(CPU_UP_PREPARE | mod, hcpu, -1, &nr_calls);
         if (ret) {
                 nr_calls--;
@@ -309,7 +363,7 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
         }
 
         /* Arch-specific enabling code. */
-        ret = __cpu_up(cpu);
+        ret = __cpu_up(cpu, idle);
         if (ret != 0)
                 goto out_notify;
         BUG_ON(!cpu_online(cpu));
@@ -320,6 +374,7 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
 out_notify:
         if (ret != 0)
                 __cpu_notify(CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
+out:
         cpu_hotplug_done();
 
         return ret;