kthread_worker: reimplement flush_kthread_work() to allow freeing the work item being executed

kthread_worker provides minimalistic workqueue-like interface for
users which need a dedicated worker thread (e.g. for realtime
priority).  It has basic queue, flush_work, flush_worker operations
which mostly match the workqueue counterparts; however, due to the way
flush_work() is implemented, it has a noticeable difference of not
allowing work items to be freed while being executed.

While the current users of kthread_worker are okay with the current
behavior, the restriction does impede some valid use cases.  Also,
removing this difference isn't difficult and actually makes the code
easier to understand.

This patch reimplements flush_kthread_work() such that it uses a
flush_work item instead of queue/done sequence numbers.

Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 2 insertions, 6 deletions

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 0714b24..22ccf9d 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -49,8 +49,6 @@ extern int tsk_fork_get_node(struct task_struct *tsk);
  * 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);
@@ -59,15 +57,14 @@ struct kthread_worker {
 	spinlock_t		lock;
 	struct list_head	work_list;
 	struct task_struct	*task;
+	struct kthread_work	*current_work;
 };
 
 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;
+	struct kthread_worker	*worker;
 };
 
 #define KTHREAD_WORKER_INIT(worker)	{				\
@@ -79,7 +76,6 @@ struct kthread_work {
 	.node = LIST_HEAD_INIT((work).node),				\
 	.func = (fn),							\
 	.done = __WAIT_QUEUE_HEAD_INITIALIZER((work).done),		\
-	.flushing = ATOMIC_INIT(0),					\
 	}
 
 #define DEFINE_KTHREAD_WORKER(worker)					\