From patchwork Sun Aug 20 01:02:19 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Qu Wenruo X-Patchwork-Id: 13358692 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 8224EEE49A3 for ; Sun, 20 Aug 2023 02:40:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229747AbjHTCkA (ORCPT ); Sat, 19 Aug 2023 22:40:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60578 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229804AbjHTCju (ORCPT ); Sat, 19 Aug 2023 22:39:50 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 56203337B7; Sat, 19 Aug 2023 18:02:39 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 171CD21872; Sun, 20 Aug 2023 01:02:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1692493358; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=G+yAUJJ/HHaqmh6NDtmiAagDlj0RVk5L96mKpGiAGOA=; b=KkW6zQOfjedMZgmyt2EvkTR96IAS6NyONSCWFYe3PZYWOoUgF9vTm23nObfCmRJ+sO6coZ K59MbzAMW0UigaLBlfvXcsdLpxhxTNIm3mgayhqGoteFzJ+0dnZRD1S+TCLONlnHOD/9LA XcvLgLHvf6rgeSmKBNNK9JLAE35RbQs= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 26D081358B; Sun, 20 Aug 2023 01:02:36 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id VNF7Nyxm4WRudgAAMHmgww (envelope-from ); Sun, 20 Aug 2023 01:02:36 +0000 From: Qu Wenruo To: linux-btrfs@vger.kernel.org, fstests@vger.kernel.org Subject: [PATCH] fstests: fsstress: wait interrupted aio to finish Date: Sun, 20 Aug 2023 09:02:19 +0800 Message-ID: <20230820010219.12907-1-wqu@suse.com> X-Mailer: git-send-email 2.41.0 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: fstests@vger.kernel.org [BUG] There is a very low chance to hit data csum mismatch (caught by scrub) during test case btrfs/06[234567]. After some extra digging, it turns out that plain fsstress itself is enough to cause the problem: ``` workload() { mkfs.btrfs -f -m single -d single --csum sha256 $dev1 > /dev/null mount $dev1 $mnt #$fsstress -p 10 -n 1000 -w -d $mnt umount $mnt btrfs check --check-data-csum $dev1 || fail } runtime=1024 for (( i = 0; i < $runtime; i++ )); do echo "=== $i / $runtime ===" workload done ``` Inside a VM which has only 6 cores, above script can trigger with 1/20 possibility. [CAUSE] Locally I got a much smaller workload to reproduce: $fsstress -p 7 -n 50 -s 1691396493 -w -d $mnt -v > /tmp/fsstress With extra kernel trace_prinkt() on the buffered/direct writes. It turns out that the following direct write is always the cause: btrfs_do_write_iter: r/i=5/283 buffered fileoff=708608(709121) len=12288(7712) btrfs_do_write_iter: r/i=5/283 direct fileoff=8192(8192) len=73728(73728) <<<<< btrfs_do_write_iter: r/i=5/283 direct fileoff=589824(589824) len=16384(16384) With the involved byte number, it's easy to pin down the fsstress opeartion: 0/31: writev d0/f3[285 2 0 0 296 1457078] [709121,8,964] 0 0/32: chown d0/f2 308134/1763236 0 0/33: do_aio_rw - xfsctl(XFS_IOC_DIOINFO) d0/f2[285 2 308134 1763236 320 1457078] return 25, fallback to stat() 0/33: awrite - io_getevents failed -4 <<<< 0/34: dwrite - xfsctl(XFS_IOC_DIOINFO) d0/f3[285 2 308134 1763236 320 1457078] return 25, fallback to stat() Note the 0/33, when the data csum mismatch triggered, it always fail with -4 (-EINTR). It looks like with lucky enough concurrency, we can get to the following situation inside fsstress: Process A | Process B -----------------------------------+--------------------------------------- do_aio_rw() | |- io_sumit(); | |- io_get_events(); | | Returned -EINTR, but IO hasn't | | finished. | `- free(buf); | malloc(); | Got the same memory of @buf from | thread A. | Modify the memory | Now the buffer is changed while | still under IO This is the typical buffer modification during direct IO, which is going to cause csum mismatch for btrfs, and btrfs properly detects it. This is the direct cause of the problem. However I'm still not 100% sure on why we got -EINTR for io_getevents(). My previous tests shows that if I disable uring_write, then no more such data corruption, thus I guess io_uring has something affecting aio? [FIX] To fix the problem, we can just retry io_getevents() so that we can properly wait for the IO. This prevents us to modify the IO buffer before writeback really finishes. With this fixes, I can no longer reproduce the data corruption. Signed-off-by: Qu Wenruo Reviewed-by: Anand Jain --- ltp/fsstress.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/ltp/fsstress.c b/ltp/fsstress.c index 6641a525..f9f132bf 100644 --- a/ltp/fsstress.c +++ b/ltp/fsstress.c @@ -2223,7 +2223,15 @@ do_aio_rw(opnum_t opno, long r, int flags) procid, opno, iswrite ? "awrite" : "aread", e); goto aio_out; } - if ((e = io_getevents(io_ctx, 1, 1, &event, NULL)) != 1) { + do { + e = io_getevents(io_ctx, 1, 1, &event, NULL); + if (e == -EINTR) { + if (v) + printf("%d/%lld: %s - io_getevents interruped %d, retrying\n", + procid, opno, iswrite ? "awrite" : "aread", e); + } + } while (e == -EINTR); + if (e != 1) { if (v) printf("%d/%lld: %s - io_getevents failed %d\n", procid, opno, iswrite ? "awrite" : "aread", e);