Merge branch 'core/urgent' into core/entry

[platform/kernel/linux-rpi.git] / kernel / task_work.c

diff --git a/kernel/task_work.c b/kernel/task_work.c
index 8d6e121..15b0872 100644 (file)
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -5,6 +5,34 @@
 
 static struct callback_head work_exited; /* all we need is ->next == NULL */
 
+/*
+ * TWA_SIGNAL signaling - use TIF_NOTIFY_SIGNAL, if available, as it's faster
+ * than TIF_SIGPENDING as there's no dependency on ->sighand. The latter is
+ * shared for threads, and can cause contention on sighand->lock. Even for
+ * the non-threaded case TIF_NOTIFY_SIGNAL is more efficient, as no locking
+ * or IRQ disabling is involved for notification (or running) purposes.
+ */
+static void task_work_notify_signal(struct task_struct *task)
+{
+#if defined(TIF_NOTIFY_SIGNAL)
+       set_notify_signal(task);
+#else
+       unsigned long flags;
+
+       /*
+        * Only grab the sighand lock if we don't already have some
+        * task_work pending. This pairs with the smp_store_mb()
+        * in get_signal(), see comment there.
+        */
+       if (!(READ_ONCE(task->jobctl) & JOBCTL_TASK_WORK) &&
+           lock_task_sighand(task, &flags)) {
+               task->jobctl |= JOBCTL_TASK_WORK;
+               signal_wake_up(task, 0);
+               unlock_task_sighand(task, &flags);
+       }
+#endif
+}
+
 /**
  * task_work_add - ask the @task to execute @work->func()
  * @task: the task which should run the callback
@@ -33,7 +61,6 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
                  enum task_work_notify_mode notify)
 {
        struct callback_head *head;
-       unsigned long flags;
 
        do {
                head = READ_ONCE(task->task_works);
@@ -49,17 +76,7 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
                set_notify_resume(task);
                break;
        case TWA_SIGNAL:
-               /*
-                * Only grab the sighand lock if we don't already have some
-                * task_work pending. This pairs with the smp_store_mb()
-                * in get_signal(), see comment there.
-                */
-               if (!(READ_ONCE(task->jobctl) & JOBCTL_TASK_WORK) &&
-                   lock_task_sighand(task, &flags)) {
-                       task->jobctl |= JOBCTL_TASK_WORK;
-                       signal_wake_up(task, 0);
-                       unlock_task_sighand(task, &flags);
-               }
+               task_work_notify_signal(task);
                break;
        default:
                WARN_ON_ONCE(1);