kthread: implement kthread_worker

Implement simple work processor for kthread.  This is to ease using
kthread.  Single thread workqueue used to be used for things like this
but workqueue won't guarantee fixed kthread association anymore to
enable worker sharing.

This can be used in cases where specific kthread association is
necessary, for example, when it should have RT priority or be assigned
to certain cgroup.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 64 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 */