Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...

[sfrench/cifs-2.6.git] / kernel / sched / core.c

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 43f44539b88f888a21f67b407d0041f3add7e948..0002995570db2120c0cf38a93bfbd50b3e478345 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -396,19 +396,7 @@ static bool set_nr_if_polling(struct task_struct *p)
 #endif
 #endif
 
-/**
- * wake_q_add() - queue a wakeup for 'later' waking.
- * @head: the wake_q_head to add @task to
- * @task: the task to queue for 'later' wakeup
- *
- * Queue a task for later wakeup, most likely by the wake_up_q() call in the
- * same context, _HOWEVER_ this is not guaranteed, the wakeup can come
- * instantly.
- *
- * This function must be used as-if it were wake_up_process(); IOW the task
- * must be ready to be woken at this location.
- */
-void wake_q_add(struct wake_q_head *head, struct task_struct *task)
+static bool __wake_q_add(struct wake_q_head *head, struct task_struct *task)
 {
        struct wake_q_node *node = &task->wake_q;
 
@@ -421,16 +409,56 @@ void wake_q_add(struct wake_q_head *head, struct task_struct *task)
         * state, even in the failed case, an explicit smp_mb() must be used.
         */
        smp_mb__before_atomic();
-       if (cmpxchg_relaxed(&node->next, NULL, WAKE_Q_TAIL))
-               return;
-
-       get_task_struct(task);
+       if (unlikely(cmpxchg_relaxed(&node->next, NULL, WAKE_Q_TAIL)))
+               return false;
 
        /*
         * The head is context local, there can be no concurrency.
         */
        *head->lastp = node;
        head->lastp = &node->next;
+       return true;
+}
+
+/**
+ * wake_q_add() - queue a wakeup for 'later' waking.
+ * @head: the wake_q_head to add @task to
+ * @task: the task to queue for 'later' wakeup
+ *
+ * Queue a task for later wakeup, most likely by the wake_up_q() call in the
+ * same context, _HOWEVER_ this is not guaranteed, the wakeup can come
+ * instantly.
+ *
+ * This function must be used as-if it were wake_up_process(); IOW the task
+ * must be ready to be woken at this location.
+ */
+void wake_q_add(struct wake_q_head *head, struct task_struct *task)
+{
+       if (__wake_q_add(head, task))
+               get_task_struct(task);
+}
+
+/**
+ * wake_q_add_safe() - safely queue a wakeup for 'later' waking.
+ * @head: the wake_q_head to add @task to
+ * @task: the task to queue for 'later' wakeup
+ *
+ * Queue a task for later wakeup, most likely by the wake_up_q() call in the
+ * same context, _HOWEVER_ this is not guaranteed, the wakeup can come
+ * instantly.
+ *
+ * This function must be used as-if it were wake_up_process(); IOW the task
+ * must be ready to be woken at this location.
+ *
+ * This function is essentially a task-safe equivalent to wake_q_add(). Callers
+ * that already hold reference to @task can call the 'safe' version and trust
+ * wake_q to do the right thing depending whether or not the @task is already
+ * queued for wakeup.
+ */
+void wake_q_add_safe(struct wake_q_head *head, struct task_struct *task)
+{
+       if (!__wake_q_add(head, task))
+               put_task_struct(task);
 }
 
 void wake_up_q(struct wake_q_head *head)
@@ -5866,14 +5894,11 @@ void __init sched_init_smp(void)
        /*
         * There's no userspace yet to cause hotplug operations; hence all the
         * CPU masks are stable and all blatant races in the below code cannot
-        * happen. The hotplug lock is nevertheless taken to satisfy lockdep,
-        * but there won't be any contention on it.
+        * happen.
         */
-       cpus_read_lock();
        mutex_lock(&sched_domains_mutex);
        sched_init_domains(cpu_active_mask);
        mutex_unlock(&sched_domains_mutex);
-       cpus_read_unlock();
 
        /* Move init over to a non-isolated CPU */
        if (set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_FLAG_DOMAIN)) < 0)