From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8A7F3C433F5 for ; Thu, 21 Apr 2022 09:14:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1387427AbiDUJRH (ORCPT ); Thu, 21 Apr 2022 05:17:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52870 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1376621AbiDUJRB (ORCPT ); Thu, 21 Apr 2022 05:17:01 -0400 Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com [67.231.145.42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 95D9C24F24 for ; Thu, 21 Apr 2022 02:14:12 -0700 (PDT) Received: from pps.filterd (m0044010.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.1.2/8.16.1.2) with ESMTP id 23L8AdK0000913 for ; Thu, 21 Apr 2022 02:14:12 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : mime-version : content-transfer-encoding : content-type; s=facebook; bh=gbTkmP4OC3+yQ08kGFbROr+SigHxueVMyVvJ18BOaGc=; b=AqFjd4BcS7L37OpSYyEDJpQrEoQO61lMqAPq3hXub5ihjhDx/GWOWoEgWl44crzz7LIe Sr3U8UJ/UygSBtU7AVoBnCJoXw7Y1/HKdGrlbP/QOXZ30vqoVQjZ+N3tBruNdaj7iBzb 2/ov/q4FvP3SGdBjg5Kyn5VzgpTe7CxsosM= Received: from mail.thefacebook.com ([163.114.132.120]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 3fj36tb6ax-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Thu, 21 Apr 2022 02:14:12 -0700 Received: from twshared8053.07.ash9.facebook.com (2620:10d:c085:208::11) by mail.thefacebook.com (2620:10d:c085:11d::4) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 21 Apr 2022 02:14:11 -0700 Received: by devbig039.lla1.facebook.com (Postfix, from userid 572232) id DD73F7CA75F8; Thu, 21 Apr 2022 02:14:01 -0700 (PDT) From: Dylan Yudaken To: CC: , , , , Dylan Yudaken Subject: [PATCH 0/6] return an error when cqe is dropped Date: Thu, 21 Apr 2022 02:13:39 -0700 Message-ID: <20220421091345.2115755-1-dylany@fb.com> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-FB-Internal: Safe Content-Type: text/plain X-Proofpoint-GUID: lTW67kSbunWPcWlvej0CVWBZZ856L57w X-Proofpoint-ORIG-GUID: lTW67kSbunWPcWlvej0CVWBZZ856L57w X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.858,Hydra:6.0.486,FMLib:17.11.64.514 definitions=2022-04-20_06,2022-04-20_01,2022-02-23_01 Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org This series addresses a rare but real error condition when a CQE is dropped. Many applications rely on 1 SQE resulting in 1 CQE and may even block waiting for the CQE. In overflow conditions if the GFP_ATOMIC allocation fails, the CQE is dropped and a counter is incremented. Howeve= r the application is not actively signalled that something bad has happened. We would like to indicate this error condition to the application but in a way that does not rely on the application doing invasive changes such as checking a flag before each wait. This series returns an error code to the application when the error hits, and then resets the error condition. If the application is ok with this error it can continue as is, or more likely it can clean up sanely. Patches 1&2 add tracing for overflows Patches 3&4 prep for adding this error Patch 5 is the main one returning an error Patch 6 allows liburing to test these conditions more easily with IOPOLL Dylan Yudaken (6): io_uring: add trace support for CQE overflow io_uring: trace cqe overflows io_uring: rework io_uring_enter to simplify return value io_uring: use constants for cq_overflow bitfield io_uring: return an error when cqe is dropped io_uring: allow NOP opcode in IOPOLL mode fs/io_uring.c | 89 ++++++++++++++++++++++----------- include/trace/events/io_uring.h | 42 +++++++++++++++- 2 files changed, 102 insertions(+), 29 deletions(-) base-commit: 7c648b7d6186c59ed3a0e0ae4b774aaf4b415ef2 --=20 2.30.2