[PATCH 1/3] io_uring: add remote task_work execution helper

[Jens Axboe <axboe@kernel.dk>]

All our task_work handling is targeted at the state in the io_kiocb
itself, which is what it is being used for. However, MSG_RING rolls its
own task_work handling, ignoring how that is usually done.

In preparation for switching MSG_RING to be able to use the normal
task_work handling, add io_req_task_work_add_remote() which allows the
caller to pass in the target io_ring_ctx and task.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/io_uring.c | 27 +++++++++++++++++++--------
 io_uring/io_uring.h |  2 ++
 2 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 9978dbe00027..609ff9ea5930 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1241,9 +1241,10 @@ void tctx_task_work(struct callback_head *cb)
 	WARN_ON_ONCE(ret);
 }
 
-static inline void io_req_local_work_add(struct io_kiocb *req, unsigned tw_flags)
+static inline void io_req_local_work_add(struct io_kiocb *req,
+					 struct io_ring_ctx *ctx,
+					 unsigned tw_flags)
 {
-	struct io_ring_ctx *ctx = req->ctx;
 	unsigned nr_wait, nr_tw, nr_tw_prev;
 	unsigned long flags;
 
@@ -1291,9 +1292,10 @@ static inline void io_req_local_work_add(struct io_kiocb *req, unsigned tw_flags
 	wake_up_state(ctx->submitter_task, TASK_INTERRUPTIBLE);
 }
 
-static void io_req_normal_work_add(struct io_kiocb *req)
+static void io_req_normal_work_add(struct io_kiocb *req,
+				   struct task_struct *task)
 {
-	struct io_uring_task *tctx = req->task->io_uring;
+	struct io_uring_task *tctx = task->io_uring;
 	struct io_ring_ctx *ctx = req->ctx;
 	unsigned long flags;
 	bool was_empty;
@@ -1319,7 +1321,7 @@ static void io_req_normal_work_add(struct io_kiocb *req)
 		return;
 	}
 
-	if (likely(!task_work_add(req->task, &tctx->task_work, ctx->notify_method)))
+	if (likely(!task_work_add(task, &tctx->task_work, ctx->notify_method)))
 		return;
 
 	io_fallback_tw(tctx, false);
@@ -1328,9 +1330,18 @@ static void io_req_normal_work_add(struct io_kiocb *req)
 void __io_req_task_work_add(struct io_kiocb *req, unsigned flags)
 {
 	if (req->ctx->flags & IORING_SETUP_DEFER_TASKRUN)
-		io_req_local_work_add(req, flags);
+		io_req_local_work_add(req, req->ctx, flags);
+	else
+		io_req_normal_work_add(req, req->task);
+}
+
+void io_req_task_work_add_remote(struct io_kiocb *req, struct task_struct *task,
+				 struct io_ring_ctx *ctx, unsigned flags)
+{
+	if (req->ctx->flags & IORING_SETUP_DEFER_TASKRUN)
+		io_req_local_work_add(req, ctx, flags);
 	else
-		io_req_normal_work_add(req);
+		io_req_normal_work_add(req, task);
 }
 
 static void __cold io_move_task_work_from_local(struct io_ring_ctx *ctx)
@@ -1349,7 +1360,7 @@ static void __cold io_move_task_work_from_local(struct io_ring_ctx *ctx)
 						    io_task_work.node);
 
 		node = node->next;
-		io_req_normal_work_add(req);
+		io_req_normal_work_add(req, req->task);
 	}
 }
 
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index bde463642c71..a6dec5321ec4 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -74,6 +74,8 @@ struct file *io_file_get_fixed(struct io_kiocb *req, int fd,
 			       unsigned issue_flags);
 
 void __io_req_task_work_add(struct io_kiocb *req, unsigned flags);
+void io_req_task_work_add_remote(struct io_kiocb *req, struct task_struct *task,
+				 struct io_ring_ctx *ctx, unsigned flags);
 bool io_alloc_async_data(struct io_kiocb *req);
 void io_req_task_queue(struct io_kiocb *req);
 void io_req_task_complete(struct io_kiocb *req, struct io_tw_state *ts);
-- 
2.43.0