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 F2C04C433EF for ; Fri, 8 Oct 2021 01:56:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C871C60F92 for ; Fri, 8 Oct 2021 01:56:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231688AbhJHB6l (ORCPT ); Thu, 7 Oct 2021 21:58:41 -0400 Received: from szxga02-in.huawei.com ([45.249.212.188]:23353 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229487AbhJHB6k (ORCPT ); Thu, 7 Oct 2021 21:58:40 -0400 Received: from dggeme754-chm.china.huawei.com (unknown [172.30.72.54]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4HQWQr3xRvzbcxj; Fri, 8 Oct 2021 09:52:20 +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 09:56:44 +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> CC: , , , From: yebin Message-ID: <615FA55B.5070404@huawei.com> Date: Fri, 8 Oct 2021 09:56:43 +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: <20211007123100.GG12712@quack2.suse.cz> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit 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 2021/10/7 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. >> --- >> 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 >>