mdadm failed to create internal bitmap

[Jonas Fisher <fisherthepooh@xxxxxxxxxxxxxx>]

Hi all,

I got a raid1 composed with 2 disks
/dev/sda -- 2T
/dev/sdb -- 4T

mdadm version is 3.3 and md metadata version is 1.0

At first, I was only using 1T of the each disk,

then I grew the array recently with the command

mdadm --grow /dev/md1 --size=1951944704K

I also tried to add the internal bitmap after expansion finished

mdadm --grow /dev/md1 --bitmap=internal

But I got the following message

mdadm: failed to create internal bitmap - chunksize problem.

I found that Avail Dev Size in superblock examine of two disks

are the same, same as the value I set when I expanded the array (1951944704K).

Then I found that in mdadm bitmap chunksize calculation,

in function add_internal_bitmap1 (super1.c)

variable "room" and and "max_bits" seems to be overflowed under this situation

/dev/sdb3:
          Magic : a92b4efc
        Version : 1.0
    Feature Map : 0x0
     Array UUID : 8d7b8858:e0e93d83:7c87e6e0:bd1628b8
           Name : 1
  Creation Time : Sun Apr  8 09:54:47 2018
     Raid Level : raid1
   Raid Devices : 2

Avail Dev Size : 3903889408 (1861.52 GiB 1998.79 GB)
     Array Size : 1951944704 (1861.52 GiB 1998.79 GB)
   Super Offset : 7810899368 sectors
   Unused Space : before=0 sectors, after=3907009952 sectors
          State : clean
    Device UUID : 3546fab2:3bfd9a17:39d78059:3d1eb830

    Update Time : Sun May 17 10:24:33 2020
  Bad Block Log : 512 entries available at offset -8 sectors
       Checksum : cf552c50 - correct
         Events : 93088


   Device Role : Active device 0
   Array State : AA ('A' == active, '.' == missing, 'R' == replacing)

/dev/sda3:
          Magic : a92b4efc
        Version : 1.0
    Feature Map : 0x0
     Array UUID : 8d7b8858:e0e93d83:7c87e6e0:bd1628b8
           Name : 1
  Creation Time : Sun Apr  8 09:54:47 2018
     Raid Level : raid1
   Raid Devices : 2

Avail Dev Size : 3903889408 (1861.52 GiB 1998.79 GB)
     Array Size : 1951944704 (1861.52 GiB 1998.79 GB)
   Super Offset : 3903891368 sectors
   Unused Space : before=0 sectors, after=1952 sectors
          State : clean
    Device UUID : 980038ac:99f4e8c6:39d91851:bdf6ed6d

    Update Time : Sun May 17 10:24:33 2020
  Bad Block Log : 512 entries available at offset -8 sectors
       Checksum : c3ce8290 - correct
         Events : 93088


   Device Role : Active device 1
   Array State : AA ('A' == active, '.' == missing, 'R' == replacing)

I was wondering is this because mdadm set the size of the rdevs in the array

before doing expansion (in function Grow_reshape)

that caused the sb->data_size not equals to actual raw device size

and consequently led to bitmap chunksize calculation error

or it is simply a data type issue.

Thanks,