io_uring: consistent naming for inline completion

Improve naming of the inline/deferred completion helper so it's
consistent with it's *_post counterpart. Add some comments and extra
lockdeps to ensure the locking is done right.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/797c619943dac06529e9d3fcb16e4c3cde6ad1a3.1655684496.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/io_uring.c

@@ -1380,7 +1380,7 @@ void io_req_task_complete(struct io_kiocb *req, bool *locked)
 	}
 
 	if (*locked)
-		io_req_add_compl_list(req);
+		io_req_complete_defer(req);
 	else
 		io_req_complete_post(req);
 }
@@ -1648,7 +1648,7 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
 
 	if (ret == IOU_OK) {
 		if (issue_flags & IO_URING_F_COMPLETE_DEFER)
-			io_req_add_compl_list(req);
+			io_req_complete_defer(req);
 		else
 			io_req_complete_post(req);
 	} else if (ret != IOU_ISSUE_SKIP_COMPLETE)

io_uring/io_uring.h

@@ -222,10 +222,18 @@ static inline void io_tw_lock(struct io_ring_ctx *ctx, bool *locked)
 	}
 }
 
-static inline void io_req_add_compl_list(struct io_kiocb *req)
+/*
+ * Don't complete immediately but use deferred completion infrastructure.
+ * Protected by ->uring_lock and can only be used either with
+ * IO_URING_F_COMPLETE_DEFER or inside a tw handler holding the mutex.
+ */
+static inline void io_req_complete_defer(struct io_kiocb *req)
+	__must_hold(&req->ctx->uring_lock)
 {
 	struct io_submit_state *state = &req->ctx->submit_state;
 
+	lockdep_assert_held(&req->ctx->uring_lock);
+
 	wq_list_add_tail(&req->comp_list, &state->compl_reqs);
 }