2 files changed, 213 insertions, 0 deletions

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index aabc8a13ba71..f93cb6979edc 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -34,4 +34,68 @@ int kthread_should_stop(void);
 int kthreadd(void *unused);
 extern struct task_struct *kthreadd_task;
 
+/*
+ * Simple work processor based on kthread.
+ *
+ * This provides easier way to make use of kthreads.  A kthread_work
+ * can be queued and flushed using queue/flush_kthread_work()
+ * respectively.  Queued kthread_works are processed by a kthread
+ * running kthread_worker_fn().
+ *
+ * A kthread_work can't be freed while it is executing.
+ */
+struct kthread_work;
+typedef void (*kthread_work_func_t)(struct kthread_work *work);
+
+struct kthread_worker {
+        spinlock_t              lock;
+        struct list_head        work_list;
+        struct task_struct      *task;
+};
+
+struct kthread_work {
+        struct list_head        node;
+        kthread_work_func_t     func;
+        wait_queue_head_t       done;
+        atomic_t                flushing;
+        int                     queue_seq;
+        int                     done_seq;
+};
+
+#define KTHREAD_WORKER_INIT(worker)     {                               \
+        .lock = SPIN_LOCK_UNLOCKED,                                     \
+        .work_list = LIST_HEAD_INIT((worker).work_list),                \
+        }
+
+#define KTHREAD_WORK_INIT(work, fn)     {                               \
+        .node = LIST_HEAD_INIT((work).node),                            \
+        .func = (fn),                                                   \
+        .done = __WAIT_QUEUE_HEAD_INITIALIZER((work).done),             \
+        .flushing = ATOMIC_INIT(0),                                     \
+        }
+
+#define DEFINE_KTHREAD_WORKER(worker)                                   \
+        struct kthread_worker worker = KTHREAD_WORKER_INIT(worker)
+
+#define DEFINE_KTHREAD_WORK(work, fn)                                   \
+        struct kthread_work work = KTHREAD_WORK_INIT(work, fn)
+
+static inline void init_kthread_worker(struct kthread_worker *worker)
+{
+        *worker = (struct kthread_worker)KTHREAD_WORKER_INIT(*worker);
+}
+
+static inline void init_kthread_work(struct kthread_work *work,
+                                     kthread_work_func_t fn)
+{
+        *work = (struct kthread_work)KTHREAD_WORK_INIT(*work, fn);
+}
+
+int kthread_worker_fn(void *worker_ptr);
+
+bool queue_kthread_work(struct kthread_worker *worker,
+                        struct kthread_work *work);
+void flush_kthread_work(struct kthread_work *work);
+void flush_kthread_worker(struct kthread_worker *worker);
+
 #endif /* _LINUX_KTHREAD_H */
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 83911c780175..8b63c7fee73b 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -14,6 +14,8 @@
 #include <linux/file.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/freezer.h>
 #include <trace/events/sched.h>
 
 static DEFINE_SPINLOCK(kthread_create_lock);
@@ -247,3 +249,150 @@ int kthreadd(void *unused)
 
         return 0;
 }
+
+/**
+ * kthread_worker_fn - kthread function to process kthread_worker
+ * @worker_ptr: pointer to initialized kthread_worker
+ *
+ * This function can be used as @threadfn to kthread_create() or
+ * kthread_run() with @worker_ptr argument pointing to an initialized
+ * kthread_worker.  The started kthread will process work_list until
+ * the it is stopped with kthread_stop().  A kthread can also call
+ * this function directly after extra initialization.
+ *
+ * Different kthreads can be used for the same kthread_worker as long
+ * as there's only one kthread attached to it at any given time.  A
+ * kthread_worker without an attached kthread simply collects queued
+ * kthread_works.
+ */
+int kthread_worker_fn(void *worker_ptr)
+{
+        struct kthread_worker *worker = worker_ptr;
+        struct kthread_work *work;
+
+        WARN_ON(worker->task);
+        worker->task = current;
+repeat:
+        set_current_state(TASK_INTERRUPTIBLE);  /* mb paired w/ kthread_stop */
+
+        if (kthread_should_stop()) {
+                __set_current_state(TASK_RUNNING);
+                spin_lock_irq(&worker->lock);
+                worker->task = NULL;
+                spin_unlock_irq(&worker->lock);
+                return 0;
+        }
+
+        work = NULL;
+        spin_lock_irq(&worker->lock);
+        if (!list_empty(&worker->work_list)) {
+                work = list_first_entry(&worker->work_list,
+                                        struct kthread_work, node);
+                list_del_init(&work->node);
+        }
+        spin_unlock_irq(&worker->lock);
+
+        if (work) {
+                __set_current_state(TASK_RUNNING);
+                work->func(work);
+                smp_wmb();      /* wmb worker-b0 paired with flush-b1 */
+                work->done_seq = work->queue_seq;
+                smp_mb();       /* mb worker-b1 paired with flush-b0 */
+                if (atomic_read(&work->flushing))
+                        wake_up_all(&work->done);
+        } else if (!freezing(current))
+                schedule();
+
+        try_to_freeze();
+        goto repeat;
+}
+EXPORT_SYMBOL_GPL(kthread_worker_fn);
+
+/**
+ * queue_kthread_work - queue a kthread_work
+ * @worker: target kthread_worker
+ * @work: kthread_work to queue
+ *
+ * Queue @work to work processor @task for async execution.  @task
+ * must have been created with kthread_worker_create().  Returns %true
+ * if @work was successfully queued, %false if it was already pending.
+ */
+bool queue_kthread_work(struct kthread_worker *worker,
+                        struct kthread_work *work)
+{
+        bool ret = false;
+        unsigned long flags;
+
+        spin_lock_irqsave(&worker->lock, flags);
+        if (list_empty(&work->node)) {
+                list_add_tail(&work->node, &worker->work_list);
+                work->queue_seq++;
+                if (likely(worker->task))
+                        wake_up_process(worker->task);
+                ret = true;
+        }
+        spin_unlock_irqrestore(&worker->lock, flags);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(queue_kthread_work);
+
+/**
+ * flush_kthread_work - flush a kthread_work
+ * @work: work to flush
+ *
+ * If @work is queued or executing, wait for it to finish execution.
+ */
+void flush_kthread_work(struct kthread_work *work)
+{
+        int seq = work->queue_seq;
+
+        atomic_inc(&work->flushing);
+
+        /*
+         * mb flush-b0 paired with worker-b1, to make sure either
+         * worker sees the above increment or we see done_seq update.
+         */
+        smp_mb__after_atomic_inc();
+
+        /* A - B <= 0 tests whether B is in front of A regardless of overflow */
+        wait_event(work->done, seq - work->done_seq <= 0);
+        atomic_dec(&work->flushing);
+
+        /*
+         * rmb flush-b1 paired with worker-b0, to make sure our caller
+         * sees every change made by work->func().
+         */
+        smp_mb__after_atomic_dec();
+}
+EXPORT_SYMBOL_GPL(flush_kthread_work);
+
+struct kthread_flush_work {
+        struct kthread_work     work;
+        struct completion       done;
+};
+
+static void kthread_flush_work_fn(struct kthread_work *work)
+{
+        struct kthread_flush_work *fwork =
+                container_of(work, struct kthread_flush_work, work);
+        complete(&fwork->done);
+}
+
+/**
+ * flush_kthread_worker - flush all current works on a kthread_worker
+ * @worker: worker to flush
+ *
+ * Wait until all currently executing or pending works on @worker are
+ * finished.
+ */
+void flush_kthread_worker(struct kthread_worker *worker)
+{
+        struct kthread_flush_work fwork = {
+                KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
+                COMPLETION_INITIALIZER_ONSTACK(fwork.done),
+        };
+
+        queue_kthread_work(worker, &fwork.work);
+        wait_for_completion(&fwork.done);
+}
+EXPORT_SYMBOL_GPL(flush_kthread_worker);