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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 76E39C433F5 for ; Fri, 8 Oct 2021 02:38:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 45C8C61053 for ; Fri, 8 Oct 2021 02:38:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236389AbhJHCka (ORCPT ); Thu, 7 Oct 2021 22:40:30 -0400 Received: from szxga01-in.huawei.com ([45.249.212.187]:27963 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229606AbhJHCk3 (ORCPT ); Thu, 7 Oct 2021 22:40:29 -0400 Received: from dggeme754-chm.china.huawei.com (unknown [172.30.72.53]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4HQXM42gKtzbn1L; Fri, 8 Oct 2021 10:34:08 +0800 (CST) Received: from [10.174.178.185] (10.174.178.185) by dggeme754-chm.china.huawei.com (10.3.19.100) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2308.8; Fri, 8 Oct 2021 10:38:31 +0800 Subject: Re: [PATCH -next v2 2/6] ext4: introduce last_check_time record previous check time To: Jan Kara References: <20210911090059.1876456-1-yebin10@huawei.com> <20210911090059.1876456-3-yebin10@huawei.com> <20211007123100.GG12712@quack2.suse.cz> <615FA55B.5070404@huawei.com> CC: , , , From: yebin Message-ID: <615FAF27.8070000@huawei.com> Date: Fri, 8 Oct 2021 10:38:31 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: <615FA55B.5070404@huawei.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.178.185] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggeme754-chm.china.huawei.com (10.3.19.100) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On 2021/10/8 9:56, yebin wrote: > > > On 2021/10/7 20:31, Jan Kara wrote: >> On Sat 11-09-21 17:00:55, Ye Bin wrote: >>> kmmpd: >>> ... >>> diff = jiffies - last_update_time; >>> if (diff > mmp_check_interval * HZ) { >>> ... >>> As "mmp_check_interval = 2 * mmp_update_interval", 'diff' always little >>> than 'mmp_update_interval', so there will never trigger detection. >>> Introduce last_check_time record previous check time. >>> >>> Signed-off-by: Ye Bin >> I think the check is there only for the case where write_mmp_block() + >> sleep took longer than mmp_check_interval. I agree that should rarely >> happen but on a really busy system it is possible and in that case we >> would >> miss updating mmp block for too long and so another node could have >> started >> using the filesystem. I actually don't see a reason why kmmpd should be >> checking the block each mmp_check_interval as you do - >> mmp_check_interval >> is just for ext4_multi_mount_protect() to know how long it should wait >> before considering mmp block stale... Am I missing something? >> >> Honza > I'm sorry, I didn't understand the detection mechanism here before. > Now I understand > the detection mechanism here. > As you said, it's just an abnormal protection. There's really no problem. > Yeah, i did test as following steps hostA hostB mount ext4_multi_mount_protect -> seq == EXT4_MMP_SEQ_CLEAN delay 5s after label "skip" so hostB will see seq is EXT4_MMP_SEQ_CLEAN mount ext4_multi_mount_protect -> seq == EXT4_MMP_SEQ_CLEAN run kmmpd run kmmpd Actually，in this situation kmmpd will not detect confliction. In ext4_multi_mount_protect function we write mmp data fisrt and wait 'wait_time * HZ' seconds, read mmp data do check.Most of the time, If 'wait_time' is zero, it can pass check. >>> --- >>> fs/ext4/mmp.c | 14 +++++++++----- >>> 1 file changed, 9 insertions(+), 5 deletions(-) >>> >>> diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c >>> index 12af6dc8457b..c781b09a78c9 100644 >>> --- a/fs/ext4/mmp.c >>> +++ b/fs/ext4/mmp.c >>> @@ -152,6 +152,7 @@ static int kmmpd(void *data) >>> int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval); >>> unsigned mmp_check_interval; >>> unsigned long last_update_time; >>> + unsigned long last_check_time; >>> unsigned long diff; >>> int retval = 0; >>> @@ -170,6 +171,7 @@ static int kmmpd(void *data) >>> memcpy(mmp->mmp_nodename, init_utsname()->nodename, >>> sizeof(mmp->mmp_nodename)); >>> + last_check_time = jiffies; >>> while (!kthread_should_stop() && !sb_rdonly(sb)) { >>> if (!ext4_has_feature_mmp(sb)) { >>> @@ -198,17 +200,18 @@ static int kmmpd(void *data) >>> } >>> diff = jiffies - last_update_time; >>> - if (diff < mmp_update_interval * HZ) >>> + if (diff < mmp_update_interval * HZ) { >>> schedule_timeout_interruptible(mmp_update_interval * >>> HZ - diff); >>> + diff = jiffies - last_update_time; >>> + } >>> /* >>> * We need to make sure that more than mmp_check_interval >>> - * seconds have not passed since writing. If that has happened >>> - * we need to check if the MMP block is as we left it. >>> + * seconds have not passed since check. If that has happened >>> + * we need to check if the MMP block is as we write it. >>> */ >>> - diff = jiffies - last_update_time; >>> - if (diff > mmp_check_interval * HZ) { >>> + if (jiffies - last_check_time > mmp_check_interval * HZ) { >>> struct buffer_head *bh_check = NULL; >>> struct mmp_struct *mmp_check; >>> @@ -234,6 +237,7 @@ static int kmmpd(void *data) >>> goto wait_to_exit; >>> } >>> put_bh(bh_check); >>> + last_check_time = jiffies; >>> } >>> /* >>> -- >>> 2.31.1 >>> >