fdisk problem on 3ware based system (6.1-RELEASE-p3)

[Michael R. Wayne]

I see to have an fdisk issue on one of our boxes with a 3ware card.  Relevant
lines from dmesg:
   twe0: <3ware Storage Controller. Driver version 1.50.01.002> port 0x9c00-0x9c0f mem 0xfc000000-0xfc7fffff irq 20 at device 1.0 on pci2
   twe0: 2 ports, Firmware FE8S 1.05.00.068, BIOS BE7X 1.08.00.048
   twed0: <Unit 0, TwinStor, Normal> on twe0
   twed0: 76318MB (156299440 sectors)

This started out because I am unable to create a new partition on
a machine running 6.1-RELEASE-p3 and am beginning to suspect something
is wrong in fdisk.  If I run sysinstall and go to the partition
editor, I get the following, which seems correct:

   Disk name:      twed0                                  FDISK Partition Editor
   DISK Geometry:  9729 cyls/255 heads/63 sectors = 156296385 sectors (76316MB)

   Offset       Size(ST)        End     Name  PType       Desc  Subtype    Flags

            0         63         62        -     12     unused        0
           63   31455207   31455269  twed0s1      8    freebsd      165
     31455270   58717575   90172844  twed0s2      8    freebsd      165
     90172845   66126595  156299439        -     12     unused        0

But, I am unable to create a third partition.  Every time I do that, I get:
   ERROR: Unable to write data to disk twed0!

This machine is not running with an elevated security level:
   kern.securelevel: -1


So, I decided to go in with fdisk and see what was up.  It looks
like fdisk is very confused on partition 2, which is likely
why I can not create a partition 3 (even using fdisk):

   > fdisk /dev/twed0
   ******* Working on device /dev/twed0 *******
   parameters extracted from in-core disklabel are:
   cylinders=9729 heads=255 sectors/track=63 (16065 blks/cyl)

   Figures below won't work with BIOS for partitions not in cyl 1
   parameters to be used for BIOS calculations are:
   cylinders=9729 heads=255 sectors/track=63 (16065 blks/cyl)

   Media sector size is 512
   Warning: BIOS sector numbering starts with sector 1
   Information from DOS bootblock is:
   The data for partition 1 is:
   sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
       start 63, size 31455207 (15358 Meg), flag 80 (active)
           beg: cyl 0/ head 1/ sector 1;
           end: cyl 1023/ head 254/ sector 63
   The data for partition 2 is:
   sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
       start 31455270, size 58717575 (28670 Meg), flag 0
           beg: cyl 1023/ head 255/ sector 63;
           end: cyl 1023/ head 254/ sector 63           <---------------- !!
   The data for partition 3 is:
   <UNUSED>
   The data for partition 4 is:
   <UNUSED>

At this point, I'm suspecting that fdisk is computing something
incorrectly and am not sure how to proceed as I'd prefer not to
corrupt my disk label.  Before I consider filing a PR, is this a
known problem?

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