WARNING: Re-reading the partition table failed with error 22: Invalid argument. - SOLVED and EXPLAINED

In case you have this WARNING while creating partition on multipath device

 WARNING: Re-reading the partition table failed with error 22: Invalid argument. 

don't panic.

# fdisk /dev/mapper/mpatha
Partition number (1-4): 1
   First cylinder (1-19074, default 1):
   Using default value 1
   Last cylinder or +size or +sizeM or +sizeK (1-19074, default 19074):
   Using default value 19074

   Command (m for help): p

   Disk /dev/mapper/mpatha: 156.8 GB, 156892397568 bytes
   255 heads, 63 sectors/track, 19074 cylinders
   Units = cylinders of 16065 * 512 = 8225280 bytes

                            Device Boot      Start         End      Blocks   Id  System
   /dev/mapper/mpathap1               1       19074   153211873+  83  Linux

   Command (m for help): w
   The partition table has been altered!

   Calling ioctl() to re-read partition table.

   WARNING: Re-reading the partition table failed with error 22: Invalid argument.  <------
   The kernel still uses the old table.
   The new table will be used at the next reboot.
   Syncing disks.

Depending on you Linux distro, there can be also suggestion that you reboot server or use parted or kpartx so that new partition table be used.

In case you have this error, first you should check if kpartx see newly created partition with

kpartx -l /dev/mapper/mpatha
mpatha1 : 0 33552384 /dev/mapper/mpatha 2048

This means that kpartx can normally see partition on multipath device mpatha. In other words, new partition table is already applied.

P.S. Don't mind the numbers on last command.