Add the rt linux 4.1.3-rt3 as base

[kvmfornfv.git] / kernel / kernel / task_work.c

diff --git a/kernel/kernel/task_work.c b/kernel/kernel/task_work.c
new file mode 100644 (file)
index 0000000..8727032
--- /dev/null
+++ b/kernel/kernel/task_work.c
@@ -0,0 +1,128 @@
+#include <linux/spinlock.h>
+#include <linux/task_work.h>
+#include <linux/tracehook.h>
+
+static struct callback_head work_exited; /* all we need is ->next == NULL */
+
+/**
+ * task_work_add - ask the @task to execute @work->func()
+ * @task: the task which should run the callback
+ * @work: the callback to run
+ * @notify: send the notification if true
+ *
+ * Queue @work for task_work_run() below and notify the @task if @notify.
+ * Fails if the @task is exiting/exited and thus it can't process this @work.
+ * Otherwise @work->func() will be called when the @task returns from kernel
+ * mode or exits.
+ *
+ * This is like the signal handler which runs in kernel mode, but it doesn't
+ * try to wake up the @task.
+ *
+ * RETURNS:
+ * 0 if succeeds or -ESRCH.
+ */
+int
+task_work_add(struct task_struct *task, struct callback_head *work, bool notify)
+{
+       struct callback_head *head;
+
+       do {
+               head = ACCESS_ONCE(task->task_works);
+               if (unlikely(head == &work_exited))
+                       return -ESRCH;
+               work->next = head;
+       } while (cmpxchg(&task->task_works, head, work) != head);
+
+       if (notify)
+               set_notify_resume(task);
+       return 0;
+}
+
+/**
+ * task_work_cancel - cancel a pending work added by task_work_add()
+ * @task: the task which should execute the work
+ * @func: identifies the work to remove
+ *
+ * Find the last queued pending work with ->func == @func and remove
+ * it from queue.
+ *
+ * RETURNS:
+ * The found work or NULL if not found.
+ */
+struct callback_head *
+task_work_cancel(struct task_struct *task, task_work_func_t func)
+{
+       struct callback_head **pprev = &task->task_works;
+       struct callback_head *work;
+       unsigned long flags;
+       /*
+        * If cmpxchg() fails we continue without updating pprev.
+        * Either we raced with task_work_add() which added the
+        * new entry before this work, we will find it again. Or
+        * we raced with task_work_run(), *pprev == NULL/exited.
+        */
+       raw_spin_lock_irqsave(&task->pi_lock, flags);
+       while ((work = ACCESS_ONCE(*pprev))) {
+               smp_read_barrier_depends();
+               if (work->func != func)
+                       pprev = &work->next;
+               else if (cmpxchg(pprev, work, work->next) == work)
+                       break;
+       }
+       raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+
+       return work;
+}
+
+/**
+ * task_work_run - execute the works added by task_work_add()
+ *
+ * Flush the pending works. Should be used by the core kernel code.
+ * Called before the task returns to the user-mode or stops, or when
+ * it exits. In the latter case task_work_add() can no longer add the
+ * new work after task_work_run() returns.
+ */
+void task_work_run(void)
+{
+       struct task_struct *task = current;
+       struct callback_head *work, *head, *next;
+
+       for (;;) {
+               /*
+                * work->func() can do task_work_add(), do not set
+                * work_exited unless the list is empty.
+                */
+               do {
+                       work = ACCESS_ONCE(task->task_works);
+                       head = !work && (task->flags & PF_EXITING) ?
+                               &work_exited : NULL;
+               } while (cmpxchg(&task->task_works, work, head) != work);
+
+               if (!work)
+                       break;
+               /*
+                * Synchronize with task_work_cancel(). It can't remove
+                * the first entry == work, cmpxchg(task_works) should
+                * fail, but it can play with *work and other entries.
+                */
+               raw_spin_unlock_wait(&task->pi_lock);
+               smp_mb();
+
+               /* Reverse the list to run the works in fifo order */
+               head = NULL;
+               do {
+                       next = work->next;
+                       work->next = head;
+                       head = work;
+                       work = next;
+               } while (work);
+
+               work = head;
+               do {
+                       next = work->next;
+                       work->func(work);
+                       work = next;
+                       cond_resched();
+               } while (work);
+       }
+}