io_uring/poll: add hash if ready poll request can't complete inline

If we don't, then we may lose access to it completely, leading to a
request leak. This will eventually stall the ring exit process as
well.

Cc: stable@vger.kernel.org
Fixes: 49f1c68e ("io_uring: optimise submission side poll_refs")
Reported-and-tested-by: syzbot+6c95df01470a47fc3af4@syzkaller.appspotmail.com
Link: https://lore.kernel.org/io-uring/0000000000009f829805f1ce87b2@google.com/Suggested-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/poll.c

@@ -533,6 +533,14 @@ static bool io_poll_can_finish_inline(struct io_kiocb *req,
 	return pt->owning || io_poll_get_ownership(req);
 }
 
+static void io_poll_add_hash(struct io_kiocb *req)
+{
+	if (req->flags & REQ_F_HASH_LOCKED)
+		io_poll_req_insert_locked(req);
+	else
+		io_poll_req_insert(req);
+}
+
 /*
  * Returns 0 when it's handed over for polling. The caller owns the requests if
  * it returns non-zero, but otherwise should not touch it. Negative values
@@ -591,18 +599,17 @@ static int __io_arm_poll_handler(struct io_kiocb *req,
 
 	if (mask &&
 	   ((poll->events & (EPOLLET|EPOLLONESHOT)) == (EPOLLET|EPOLLONESHOT))) {
-		if (!io_poll_can_finish_inline(req, ipt))
+		if (!io_poll_can_finish_inline(req, ipt)) {
+			io_poll_add_hash(req);
 			return 0;
+		}
 		io_poll_remove_entries(req);
 		ipt->result_mask = mask;
 		/* no one else has access to the req, forget about the ref */
 		return 1;
 	}
 
-	if (req->flags & REQ_F_HASH_LOCKED)
-		io_poll_req_insert_locked(req);
-	else
-		io_poll_req_insert(req);
+	io_poll_add_hash(req);
 
 	if (mask && (poll->events & EPOLLET) &&
 	    io_poll_can_finish_inline(req, ipt)) {