io_uring: complete all requests in task context

This patch adds ctx->task_complete flag. If set, we'll complete all
requests in the context of the original task. Note, this extends to
completion CQE posting only but not io_kiocb cleanup / free, e.g. io-wq
may free the requests in the free calllback. This flag will be used
later for optimisations purposes.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/21ece72953f76bb2e77659a72a14326227ab6460.1670384893.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/io_uring.h

@@ -11,6 +11,8 @@ enum io_uring_cmd_flags {
 	IO_URING_F_UNLOCKED		= 2,
 	/* the request is executed from poll, it should not be freed */
 	IO_URING_F_MULTISHOT		= 4,
+	/* executed by io-wq */
+	IO_URING_F_IOWQ			= 8,
 	/* int's last bit, sign checks are usually faster than a bit test */
 	IO_URING_F_NONBLOCK		= INT_MIN,
 

include/linux/io_uring_types.h

@@ -208,6 +208,8 @@ struct io_ring_ctx {
 		unsigned int		drain_disabled: 1;
 		unsigned int		has_evfd: 1;
 		unsigned int		syscall_iopoll: 1;
+		/* all CQEs should be posted only by the submitter task */
+		unsigned int		task_complete: 1;
 	} ____cacheline_aligned_in_smp;
 
 	/* submission data */

io_uring/io_uring.c

@@ -921,8 +921,11 @@ static void __io_req_complete_post(struct io_kiocb *req)
 
 void io_req_complete_post(struct io_kiocb *req, unsigned issue_flags)
 {
-	if (!(issue_flags & IO_URING_F_UNLOCKED) ||
-	    !(req->ctx->flags & IORING_SETUP_IOPOLL)) {
+	if (req->ctx->task_complete && (issue_flags & IO_URING_F_IOWQ)) {
+		req->io_task_work.func = io_req_task_complete;
+		io_req_task_work_add(req);
+	} else if (!(issue_flags & IO_URING_F_UNLOCKED) ||
+		   !(req->ctx->flags & IORING_SETUP_IOPOLL)) {
 		__io_req_complete_post(req);
 	} else {
 		struct io_ring_ctx *ctx = req->ctx;
@@ -1830,7 +1833,7 @@ void io_wq_submit_work(struct io_wq_work *work)
 {
 	struct io_kiocb *req = container_of(work, struct io_kiocb, work);
 	const struct io_op_def *def = &io_op_defs[req->opcode];
-	unsigned int issue_flags = IO_URING_F_UNLOCKED;
+	unsigned int issue_flags = IO_URING_F_UNLOCKED | IO_URING_F_IOWQ;
 	bool needs_poll = false;
 	int ret = 0, err = -ECANCELED;
 
@@ -3490,6 +3493,11 @@ static __cold int io_uring_create(unsigned entries, struct io_uring_params *p,
 	if (!ctx)
 		return -ENOMEM;
 
+	if ((ctx->flags & IORING_SETUP_DEFER_TASKRUN) &&
+	    !(ctx->flags & IORING_SETUP_IOPOLL) &&
+	    !(ctx->flags & IORING_SETUP_SQPOLL))
+		ctx->task_complete = true;
+
 	/*
 	 * When SETUP_IOPOLL and SETUP_SQPOLL are both enabled, user
 	 * space applications don't need to do io completion events