[PATCH 4/7] io_uring/msg_ring: avoid double indirection task_work for fd passing

[Jens Axboe <axboe@kernel.dk>]

Like what was done for MSG_RING data passing avoiding a double task_work
roundtrip for IORING_SETUP_DEFER_TASKRUN, implement the same model for
fd passing. File descriptor passing is separately locked anyway, so the
only remaining issue is CQE posting, just like it was for data passing.
And for that, we can use the same approach.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/msg_ring.c | 58 +++++++++++++++++++++++++--------------------
 1 file changed, 32 insertions(+), 26 deletions(-)

diff --git a/io_uring/msg_ring.c b/io_uring/msg_ring.c
index bdb935ef7aa2..74590e66d7f7 100644
--- a/io_uring/msg_ring.c
+++ b/io_uring/msg_ring.c
@@ -71,22 +71,6 @@ static inline bool io_msg_need_remote(struct io_ring_ctx *target_ctx)
 	return target_ctx->task_complete;
 }
 
-static int io_msg_exec_remote(struct io_kiocb *req, task_work_func_t func)
-{
-	struct io_ring_ctx *ctx = req->file->private_data;
-	struct io_msg *msg = io_kiocb_to_cmd(req, struct io_msg);
-	struct task_struct *task = READ_ONCE(ctx->submitter_task);
-
-	if (unlikely(!task))
-		return -EOWNERDEAD;
-
-	init_task_work(&msg->tw, func);
-	if (task_work_add(task, &msg->tw, TWA_SIGNAL))
-		return -EOWNERDEAD;
-
-	return IOU_ISSUE_SKIP_COMPLETE;
-}
-
 static struct io_overflow_cqe *io_alloc_overflow(struct io_ring_ctx *target_ctx)
 {
 	bool is_cqe32 = target_ctx->flags & IORING_SETUP_CQE32;
@@ -236,17 +220,39 @@ static int io_msg_install_complete(struct io_kiocb *req, unsigned int issue_flag
 	return ret;
 }
 
-static void io_msg_tw_fd_complete(struct callback_head *head)
+static int io_msg_install_remote(struct io_kiocb *req, unsigned int issue_flags,
+				 struct io_ring_ctx *target_ctx)
 {
-	struct io_msg *msg = container_of(head, struct io_msg, tw);
-	struct io_kiocb *req = cmd_to_io_kiocb(msg);
-	int ret = -EOWNERDEAD;
+	struct io_msg *msg = io_kiocb_to_cmd(req, struct io_msg);
+	bool skip_cqe = msg->flags & IORING_MSG_RING_CQE_SKIP;
+	struct io_overflow_cqe *ocqe = NULL;
+	int ret;
 
-	if (!(current->flags & PF_EXITING))
-		ret = io_msg_install_complete(req, IO_URING_F_UNLOCKED);
-	if (ret < 0)
-		req_set_fail(req);
-	io_req_queue_tw_complete(req, ret);
+	if (!skip_cqe) {
+		ocqe = io_alloc_overflow(target_ctx);
+		if (!ocqe)
+			return -ENOMEM;
+	}
+
+	if (unlikely(io_double_lock_ctx(target_ctx, issue_flags))) {
+		kfree(ocqe);
+		return -EAGAIN;
+	}
+
+	ret = __io_fixed_fd_install(target_ctx, msg->src_file, msg->dst_fd);
+	mutex_unlock(&target_ctx->uring_lock);
+
+	if (ret >= 0) {
+		msg->src_file = NULL;
+		req->flags &= ~REQ_F_NEED_CLEANUP;
+		if (!skip_cqe) {
+			spin_lock(&target_ctx->completion_lock);
+			io_msg_add_overflow(msg, target_ctx, ocqe, ret, 0);
+			return 0;
+		}
+	}
+	kfree(ocqe);
+	return ret;
 }
 
 static int io_msg_send_fd(struct io_kiocb *req, unsigned int issue_flags)
@@ -271,7 +277,7 @@ static int io_msg_send_fd(struct io_kiocb *req, unsigned int issue_flags)
 	}
 
 	if (io_msg_need_remote(target_ctx))
-		return io_msg_exec_remote(req, io_msg_tw_fd_complete);
+		return io_msg_install_remote(req, issue_flags, target_ctx);
 	return io_msg_install_complete(req, issue_flags);
 }
 
-- 
2.43.0