Merge branch 'for-3.5-take-2' of git://linux-nfs.org/~bfields/linux

[pandora-kernel.git] / kernel / cpu.c

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 0e6353c..a4eb522 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -10,7 +10,10 @@
 #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>
@@ -173,6 +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;