io_uring: fix timeout cancel return code

When we cancel a timeout we should emit a sensible return code, like
-ECANCELED but not 0, otherwise it may trick users.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/7b0ad1065e3bd1994722702bd0ba9e7bc9b0683b.1616696997.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -1247,7 +1247,7 @@ static void io_queue_async_work(struct io_kiocb *req)
 		io_queue_linked_timeout(link);
 }
 
-static void io_kill_timeout(struct io_kiocb *req)
+static void io_kill_timeout(struct io_kiocb *req, int status)
 {
 	struct io_timeout_data *io = req->async_data;
 	int ret;
@@ -1257,7 +1257,7 @@ static void io_kill_timeout(struct io_kiocb *req)
 		atomic_set(&req->ctx->cq_timeouts,
 			atomic_read(&req->ctx->cq_timeouts) + 1);
 		list_del_init(&req->timeout.list);
-		io_cqring_fill_event(req, 0);
+		io_cqring_fill_event(req, status);
 		io_put_req_deferred(req, 1);
 	}
 }
@@ -1274,7 +1274,7 @@ static bool io_kill_timeouts(struct io_ring_ctx *ctx, struct task_struct *tsk,
 	spin_lock_irq(&ctx->completion_lock);
 	list_for_each_entry_safe(req, tmp, &ctx->timeout_list, timeout.list) {
 		if (io_match_task(req, tsk, files)) {
-			io_kill_timeout(req);
+			io_kill_timeout(req, -ECANCELED);
 			canceled++;
 		}
 	}
@@ -1326,7 +1326,7 @@ static void io_flush_timeouts(struct io_ring_ctx *ctx)
 			break;
 
 		list_del_init(&req->timeout.list);
-		io_kill_timeout(req);
+		io_kill_timeout(req, 0);
 	} while (!list_empty(&ctx->timeout_list));
 
 	ctx->cq_last_tm_flush = seq;