Re: [PATCH 5.12 v3] io_uring: fix rw req completion

[Pavel Begunkov <asml.silence@gmail.com>]

On 08/04/2021 19:28, Pavel Begunkov wrote:
> WARNING: at fs/io_uring.c:8578 io_ring_exit_work.cold+0x0/0x18
> 
> As reissuing is now passed back by REQ_F_REISSUE and kiocb_done()
> internally uses __io_complete_rw(), it may stop after setting the flag
> so leaving a dangling request.
> 
> There are tricky edge cases, e.g. reading beyound file, boundary, so
> the easiest way is to hand code reissue in kiocb_done() as
> __io_complete_rw() was doing for us before.

fwiw, was using this fixed up version for 5.13


diff --git a/fs/io_uring.c b/fs/io_uring.c
index 959df7666d45..a1de599dce55 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2743,6 +2743,7 @@ static void kiocb_done(struct kiocb *kiocb, ssize_t ret,
 {
 	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw.kiocb);
 	struct io_async_rw *io = req->async_data;
+	bool check_reissue = kiocb->ki_complete == io_complete_rw;
 
 	/* add previously done IO, if any */
 	if (io && io->bytes_done > 0) {
@@ -2758,6 +2759,22 @@ static void kiocb_done(struct kiocb *kiocb, ssize_t ret,
 		__io_complete_rw(req, ret, 0, issue_flags);
 	else
 		io_rw_done(kiocb, ret);
+
+	if (check_reissue && req->flags & REQ_F_REISSUE) {
+		req->flags &= ~REQ_F_REISSUE;
+
+		if (io_resubmit_prep(req)) {
+			req_ref_get(req);
+			io_queue_async_work(req);
+		} else {
+			int cflags = 0;
+
+			req_set_fail_links(req);
+			if (req->flags & REQ_F_BUFFER_SELECTED)
+				cflags = io_put_rw_kbuf(req);
+			__io_req_complete(req, issue_flags, ret, cflags);
+		}
+	}
 }
 
 static int io_import_fixed(struct io_kiocb *req, int rw, struct iov_iter *iter)