Re: [PATCH -next v2 2/6] ext4: introduce last_check_time record previous check time
From: Jan Kara <jack@suse.cz>
Date: 2021-10-07 12:31:06
Also in:
lkml
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 <redacted>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
quoted hunk ↗ jump to hunk
--- 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
-- Jan Kara [off-list ref] SUSE Labs, CR