io_uring: kbuf: fix bug of not consuming ring buffer in partial io case

When we use ring-mapped provided buffer, we should consume it before
arm poll if partial io has been done. Otherwise the buffer may be used
by other requests and thus we lost the data.

Fixes: c7fb1942 ("io_uring: add support for ring mapped supplied buffers")
Signed-off-by: Hao Xu <howeyxu@tencent.com>
[pavel: 5.19 rebase]
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>

fs/io_uring.c

@@ -1729,9 +1729,16 @@ static void io_kbuf_recycle(struct io_kiocb *req, unsigned issue_flags)
 
 	if (!(req->flags & (REQ_F_BUFFER_SELECTED|REQ_F_BUFFER_RING)))
 		return;
-	/* don't recycle if we already did IO to this buffer */
-	if (req->flags & REQ_F_PARTIAL_IO)
+	/*
+	 * For legacy provided buffer mode, don't recycle if we already did
+	 * IO to this buffer. For ring-mapped provided buffer mode, we should
+	 * increment ring->head to explicitly monopolize the buffer to avoid
+	 * multiple use.
+	 */
+	if ((req->flags & REQ_F_BUFFER_SELECTED) &&
+	    (req->flags & REQ_F_PARTIAL_IO))
 		return;
+
 	/*
 	 * We don't need to recycle for REQ_F_BUFFER_RING, we can just clear
 	 * the flag and hence ensure that bl->head doesn't get incremented.
@@ -1739,8 +1746,13 @@ static void io_kbuf_recycle(struct io_kiocb *req, unsigned issue_flags)
 	 */
 	if (req->flags & REQ_F_BUFFER_RING) {
 		if (req->buf_list) {
-			req->buf_index = req->buf_list->bgid;
-			req->flags &= ~REQ_F_BUFFER_RING;
+			if (req->flags & REQ_F_PARTIAL_IO) {
+				req->buf_list->head++;
+				req->buf_list = NULL;
+			} else {
+				req->buf_index = req->buf_list->bgid;
+				req->flags &= ~REQ_F_BUFFER_RING;
+			}
 		}
 		return;
 	}