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 C47F1C433F5 for ; Fri, 8 Oct 2021 01:50:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 96F7A6121F for ; Fri, 8 Oct 2021 01:50:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230398AbhJHBwl (ORCPT ); Thu, 7 Oct 2021 21:52:41 -0400 Received: from szxga02-in.huawei.com ([45.249.212.188]:23352 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229487AbhJHBwk (ORCPT ); Thu, 7 Oct 2021 21:52:40 -0400 Received: from dggeme754-chm.china.huawei.com (unknown [172.30.72.53]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4HQWHw6w5vzYfNN; Fri, 8 Oct 2021 09:46:20 +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 09:50:44 +0800 Subject: Re: [PATCH -next v2 1/6] ext4: init seq with random value in kmmpd To: Jan Kara References: <20210911090059.1876456-1-yebin10@huawei.com> <20210911090059.1876456-2-yebin10@huawei.com> <20211007122604.GF12712@quack2.suse.cz> CC: , , , From: yebin Message-ID: <615FA3F4.30406@huawei.com> Date: Fri, 8 Oct 2021 09:50:44 +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: <20211007122604.GF12712@quack2.suse.cz> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.178.185] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) 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 20:26, Jan Kara wrote: > On Sat 11-09-21 17:00:54, Ye Bin wrote: >> If two host has the same nodename, and seq start from 0, May cause the >> detection mechanism to fail. >> So init seq with random value to accelerate conflict detection. >> >> Signed-off-by: Ye Bin > Thanks for the patch. I agree the code in kmmpd looks suspicious. The > sequence number is initialized to a random number in > ext4_multi_mount_protect() which is called before kmmpd is started. I think > kmmpd() should initialize its 'seq' to a number fetched from the mmp > block, instead of 0 as is currently in the code. I don't think generating a > new random number as you do is really needed... > > Honza Thank you for your advice，i will fix it. > >> --- >> fs/ext4/mmp.c | 32 ++++++++++++++++---------------- >> 1 file changed, 16 insertions(+), 16 deletions(-) >> >> diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c >> index cebea4270817..12af6dc8457b 100644 >> --- a/fs/ext4/mmp.c >> +++ b/fs/ext4/mmp.c >> @@ -122,6 +122,21 @@ void __dump_mmp_msg(struct super_block *sb, struct mmp_struct *mmp, >> (int)sizeof(mmp->mmp_bdevname), mmp->mmp_bdevname); >> } >> >> +/* >> + * Get a random new sequence number but make sure it is not greater than >> + * EXT4_MMP_SEQ_MAX. >> + */ >> +static unsigned int mmp_new_seq(void) >> +{ >> + u32 new_seq; >> + >> + do { >> + new_seq = prandom_u32(); >> + } while (new_seq > EXT4_MMP_SEQ_MAX); >> + >> + return new_seq; >> +} >> + >> /* >> * kmmpd will update the MMP sequence every s_mmp_update_interval seconds >> */ >> @@ -132,7 +147,7 @@ static int kmmpd(void *data) >> struct buffer_head *bh = EXT4_SB(sb)->s_mmp_bh; >> struct mmp_struct *mmp; >> ext4_fsblk_t mmp_block; >> - u32 seq = 0; >> + u32 seq = mmp_new_seq(); >> unsigned long failed_writes = 0; >> int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval); >> unsigned mmp_check_interval; >> @@ -258,21 +273,6 @@ void ext4_stop_mmpd(struct ext4_sb_info *sbi) >> } >> } >> >> -/* >> - * Get a random new sequence number but make sure it is not greater than >> - * EXT4_MMP_SEQ_MAX. >> - */ >> -static unsigned int mmp_new_seq(void) >> -{ >> - u32 new_seq; >> - >> - do { >> - new_seq = prandom_u32(); >> - } while (new_seq > EXT4_MMP_SEQ_MAX); >> - >> - return new_seq; >> -} >> - >> /* >> * Protect the filesystem from being mounted more than once. >> */ >> -- >> 2.31.1 >>