Re: [PATCH v5 1/2] md-cluster: fix safemode_delay value when converting to clustered bitmap

["heming.zhao@suse.com" <heming.zhao@suse.com>]

On 7/21/20 4:35 PM, Guoqing Jiang wrote:
> 
> 
> On 7/20/20 8:08 PM, Zhao Heming wrote:
>> When array convert to clustered bitmap, the safe_mode_delay doesn't
>> clean and vice versa. the /sys/block/mdX/md/safe_mode_delay keep original
>> value after changing bitmap type. In safe_delay_store(), the code forbids
>> setting mddev->safemode_delay when array is clustered. So in cluster-md
>> env, the expected safemode_delay value should be 0.
>>
>> Reproducible steps:
>> ```
>> node1 # mdadm --zero-superblock /dev/sd{b,c,d}
>> node1 # mdadm -C /dev/md0 -b internal -e 1.2 -n 2 -l mirror /dev/sdb /dev/sdc
>> node1 # cat /sys/block/md0/md/safe_mode_delay
>> 0.204
>> node1 # mdadm -G /dev/md0 -b none
>> node1 # mdadm --grow /dev/md0 --bitmap=clustered
>> node1 # cat /sys/block/md0/md/safe_mode_delay
>> 0.204  <== doesn't change, should ZERO for cluster-md
>>
>> node1 # mdadm --zero-superblock /dev/sd{b,c,d}
>> node1 # mdadm -C /dev/md0 -b clustered -e 1.2 -n 2 -l mirror /dev/sdb /dev/sdc
>> node1 # cat /sys/block/md0/md/safe_mode_delay
>> 0.000
>> node1 # mdadm -G /dev/md0 -b none
>> node1 # cat /sys/block/md0/md/safe_mode_delay
>> 0.000  <== doesn't change, should default value
>> ```
>>
>> Signed-off-by: Zhao Heming <heming.zhao@suse.com>
>> ---
>>   drivers/md/md.c | 11 +++++++++--
>>   1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/md/md.c b/drivers/md/md.c
>> index f567f536b529..1bde3df3fa18 100644
>> --- a/drivers/md/md.c
>> +++ b/drivers/md/md.c
>> @@ -101,6 +101,8 @@ static void mddev_detach(struct mddev *mddev);
>>    * count by 2 for every hour elapsed between read errors.
>>    */
>>   #define MD_DEFAULT_MAX_CORRECTED_READ_ERRORS 20
>> +/* Default safemode delay: 200 msec */
>> +#define DEFAULT_SAFEMODE_DELAY ((200 * HZ)/1000 +1)
>>   /*
>>    * Current RAID-1,4,5 parallel reconstruction 'guaranteed speed limit'
>>    * is 1000 KB/sec, so the extra system load does not show up that much.
>> @@ -5982,7 +5984,7 @@ int md_run(struct mddev *mddev)
>>       if (mddev_is_clustered(mddev))
>>           mddev->safemode_delay = 0;
>>       else
>> -        mddev->safemode_delay = (200 * HZ)/1000 +1; /* 200 msec delay */
>> +        mddev->safemode_delay = DEFAULT_SAFEMODE_DELAY;
>>       mddev->in_sync = 1;
>>       smp_wmb();
>>       spin_lock(&mddev->lock);
>> @@ -7361,6 +7363,7 @@ static int update_array_info(struct mddev *mddev, mdu_array_info_t *info)
>>                   mddev->bitmap_info.nodes = 0;
>>                   md_cluster_ops->leave(mddev);
>> +                mddev->safemode_delay = DEFAULT_SAFEMODE_DELAY;
>>               }
> 
> Not about the patch itself, just confuse about the meaning of safemode_delay.
> As safemode_delay represents 200 ms delay, but md_write_end has this.
> 
>                  /* The roundup() ensures this only performs locking once
>                   * every ->safemode_delay *jiffies*
>                   */
>                  mod_timer(&mddev->safemode_timer,
>                            roundup(jiffies, mddev->safemode_delay) +
>                            mddev->safemode_delay);
> 
> And the second argument in mod_timer() means "new timeout in jiffies",
> does the above need to convert from ms to jiffies? Am I miss something?
> 
> Thanks,
> Guoqing
> 

The safemode_delay stores jiffies not msec. it converts to ms only in safe_delay_{store|show}.
please see default value:
#define DEFAULT_SAFEMODE_DELAY ((200 * HZ)/1000 +1)
in safe_delay_store, user space input will multiple 10^3, which will convert from second to msec.
then  (*HZ/1000) to jiffies.