Messages in this thread | | | Subject | Re: [PATCH -next v2 2/6] ext4: introduce last_check_time record previous check time | From | yebin <> | Date | Fri, 8 Oct 2021 09:56:43 +0800 |
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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.
>> --- >> 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 >>
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