From: Jan Kara <jack@suse.cz>
To: yebin <yebin10@huawei.com>
Cc: Jan Kara <jack@suse.cz>,
tytso@mit.edu, adilger.kernel@dilger.ca,
linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH -next v2 2/6] ext4: introduce last_check_time record previous check time
Date: Tue, 12 Oct 2021 10:47:27 +0200 [thread overview]
Message-ID: <20211012084727.GF9697@quack2.suse.cz> (raw)
In-Reply-To: <615FAF27.8070000@huawei.com>
On Fri 08-10-21 10:38:31, yebin wrote:
> 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 <yebin10@huawei.com>
> > > 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 first and wait
> 'wait_time * HZ' seconds,
> read mmp data do check. Most of the time, If 'wait_time' is zero, it can pass
> check.
But how can be wait_time zero? As far as I'm reading the code, wait_time
must be at least EXT4_MMP_MIN_CHECK_INTERVAL...
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2021-10-12 8:47 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-11 9:00 [PATCH -next v2 0/6] Fix some issues about mmp Ye Bin
2021-09-11 9:00 ` [PATCH -next v2 1/6] ext4: init seq with random value in kmmpd Ye Bin
2021-10-07 12:26 ` Jan Kara
2021-10-08 1:50 ` yebin
2021-09-11 9:00 ` [PATCH -next v2 2/6] ext4: introduce last_check_time record previous check time Ye Bin
2021-10-07 12:31 ` Jan Kara
2021-10-08 1:56 ` yebin
2021-10-08 2:38 ` yebin
2021-10-12 8:47 ` Jan Kara [this message]
2021-10-12 11:46 ` yebin
2021-10-13 9:38 ` Jan Kara
2021-10-13 12:33 ` yebin
2021-10-13 21:41 ` Theodore Ts'o
2021-10-15 3:21 ` Andreas Dilger
2021-10-15 3:21 ` Andreas Dilger
2021-09-11 9:00 ` [PATCH -next v2 3/6] ext4: compare to local seq and nodename when check conflict Ye Bin
2021-10-07 12:36 ` Jan Kara
2021-09-11 9:00 ` [PATCH -next v2 4/6] ext4: avoid to re-read mmp check data get from page cache Ye Bin
2021-10-07 12:44 ` Jan Kara
2021-10-08 3:52 ` yebin
2021-09-11 9:00 ` [PATCH -next v2 5/6] ext4: avoid to double free s_mmp_bh Ye Bin
2021-09-11 9:00 ` [PATCH -next v2 6/6] ext4: fix possible store wrong check interval value in disk when umount Ye Bin
2021-10-07 13:12 ` Jan Kara
2021-10-08 3:49 ` yebin
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