io_uring: alloc req only after getting sqe

As io_get_sqe() split into 2 stage get/consume, get an sqe before
allocating io_kiocb, so no free_req*() for a failure case is needed,
and inline back __io_req_do_free(), which has only 1 user.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -1354,14 +1354,6 @@ static inline void io_put_file(struct io_kiocb *req, struct file *file,
 		fput(file);
 }
 
-static void __io_req_do_free(struct io_kiocb *req)
-{
-	if (likely(!io_is_fallback_req(req)))
-		kmem_cache_free(req_cachep, req);
-	else
-		clear_bit_unlock(0, (unsigned long *) req->ctx->fallback_req);
-}
-
 static void __io_req_aux_free(struct io_kiocb *req)
 {
 	if (req->flags & REQ_F_NEED_CLEANUP)
@@ -1392,7 +1384,10 @@ static void __io_free_req(struct io_kiocb *req)
 	}
 
 	percpu_ref_put(&req->ctx->refs);
-	__io_req_do_free(req);
+	if (likely(!io_is_fallback_req(req)))
+		kmem_cache_free(req_cachep, req);
+	else
+		clear_bit_unlock(0, (unsigned long *) req->ctx->fallback_req);
 }
 
 struct req_batch {
@@ -5844,18 +5839,17 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
 		struct io_kiocb *req;
 		int err;
 
+		sqe = io_get_sqe(ctx);
+		if (unlikely(!sqe)) {
+			io_consume_sqe(ctx);
+			break;
+		}
 		req = io_get_req(ctx, statep);
 		if (unlikely(!req)) {
 			if (!submitted)
 				submitted = -EAGAIN;
 			break;
 		}
-		sqe = io_get_sqe(ctx);
-		if (!sqe) {
-			__io_req_do_free(req);
-			io_consume_sqe(ctx);
-			break;
-		}
 
 		/*
 		 * All io need record the previous position, if LINK vs DARIN,