io_uring: fix sporadic double CQE entry for close

We punt close to async for the final fput(), but we log the completion
even before that even in that case. We rely on the request not having
a files table assigned to detect what the final async close should do.
However, if we punt the async queue to __io_queue_sqe(), we'll get
->files assigned and this makes io_close_finish() think it should both
close the filp again (which does no harm) AND log a new CQE event for
this request. This causes duplicate CQEs.

Queue the request up for async manually so we don't grab files
needlessly and trigger this condition.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -2843,16 +2843,13 @@ static void io_close_finish(struct io_wq_work **workptr)
 		int ret;
 
 		ret = filp_close(req->close.put_file, req->work.files);
-		if (ret < 0) {
+		if (ret < 0)
 			req_set_fail_links(req);
-		}
 		io_cqring_add_event(req, ret);
 	}
 
 	fput(req->close.put_file);
 
-	/* we bypassed the re-issue, drop the submission reference */
-	io_put_req(req);
 	io_put_req_find_next(req, &nxt);
 	if (nxt)
 		io_wq_assign_next(workptr, nxt);
@@ -2894,7 +2891,13 @@ static int io_close(struct io_kiocb *req, struct io_kiocb **nxt,
 
 eagain:
 	req->work.func = io_close_finish;
-	return -EAGAIN;
+	/*
+	 * Do manual async queue here to avoid grabbing files - we don't
+	 * need the files, and it'll cause io_close_finish() to close
+	 * the file again and cause a double CQE entry for this request
+	 */
+	io_queue_async_work(req);
+	return 0;
 }
 
 static int io_prep_sfr(struct io_kiocb *req, const struct io_uring_sqe *sqe)