From: yebin <yebin10@huawei.com>
To: Jan Kara <jack@suse.cz>
Cc: <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: Fri, 8 Oct 2021 10:38:31 +0800 [thread overview]
Message-ID: <615FAF27.8070000@huawei.com> (raw)
In-Reply-To: <615FA55B.5070404@huawei.com>
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 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
>>>
>
next prev parent reply other threads:[~2021-10-08 2:38 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 [this message]
2021-10-12 8:47 ` Jan Kara
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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