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@xxxxxxxxxx>
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
> ---
> 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 <jack@xxxxxxxx>
SUSE Labs, CR
