Re: [PATCH] io_uring: Fix LINK_TIMEOUT checks

[Jens Axboe <axboe@kernel.dk>]

On 11/14/19 2:25 PM, Jens Axboe wrote:
> On 11/14/19 2:20 PM, Pavel Begunkov wrote:
>> If IORING_OP_LINK_TIMEOUT request is a head of a link or an individual
>> request, pass it further through the submission path, where it will
>> eventually fail in __io_submit_sqe(). So respecting links and drains.
>>
>> The case, which is really need to be checked, is if a
>> IORING_OP_LINK_TIMEOUT request is 3rd or later in a link, that is
>> invalid from the user API perspective (judging by the code). Moreover,
>> put/free and friends will try to io_link_cancel_timeout() such request,
>> even though it wasn't initialised.
> 
> Care to add a test case for these to liburings test/link-timeout.c?

Wrote some test cases, I think that io_req_link_next() is just wrong.
The below should correct it. We shouldn't loop here at all, just find
the first one. That'll start that guy, sequence will continue, etc.

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 5ad652fa24b8..3230da399681 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -858,7 +858,7 @@ static void io_req_link_next(struct io_kiocb *req, struct io_kiocb **nxtptr)
 	 * safe side.
 	 */
 	nxt = list_first_entry_or_null(&req->link_list, struct io_kiocb, list);
-	while (nxt) {
+	if (nxt) {
 		list_del_init(&nxt->list);
 		if (!list_empty(&req->link_list)) {
 			INIT_LIST_HEAD(&nxt->link_list);
@@ -876,12 +876,12 @@ static void io_req_link_next(struct io_kiocb *req, struct io_kiocb **nxtptr)
 			/* we dropped this link, get next */
 			nxt = list_first_entry_or_null(&req->link_list,
 							struct io_kiocb, list);
-		} else if (nxtptr && io_wq_current_is_worker()) {
-			*nxtptr = nxt;
-			break;
-		} else {
-			io_queue_async_work(nxt);
-			break;
+		}
+		if (nxt) {
+			if (nxtptr && io_wq_current_is_worker())
+				*nxtptr = nxt;
+			else
+				io_queue_async_work(nxt);
 		}
 	}
 
-- 
Jens Axboe