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Date:   Thu, 9 Sep 2021 10:20:17 +0800
From:   Guoqing Jiang <guoqing.jiang@...ux.dev>
To:     Ye Bin <yebin10@...wei.com>, tytso@....edu,
        adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, jack@...e.cz
Subject: Re: [PATCH -next 2/6] ext4: introduce last_check_time record previous
 check time



On 9/6/21 10:47 PM, 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@...wei.com>
> ---
>   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..89797f12a815 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_update_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) {

Before the above checking, seems last_check_time is not initialized yet.
>   			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;
>   		}
>   
>   		 /*

Thanks,
Guoqing

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