Bug#855235: mdadm --size -G: size is truncated below 4TiB (on a 32bit platform)

[G.raud]

Package: mdadm
Version: 3.3.2-5+deb8u1
Severity: normal

On a raid5 array with 4 components (array size 5778520512KiB, used dev
size 1932563136KiB):

------
# mdadm --grow --size 11557041024 /dev/md/entrepot
mdadm: component size of /dev/md/entrepot unchanged at 1932563136K
unfreeze
# mdadm --grow --size 5778520512 /dev/md/entrepot ## BUG
mdadm: component size of /dev/md/entrepot has been set to 1483553216K
unfreeze
# mdadm --grow --size 1932563136K /dev/md/entrepot
mdadm: component size of /dev/md/entrepot has been set to 1932563136K
unfreeze
# mdadm -G --size 3500G /dev/md/entrepot                                                             
mdadm: component size of /dev/md/entrepot unchanged at 1932563136K
unfreeze
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In the second case the size of ~5,3TiB is truncated to 1,3TiB (-4TiB).
In the first case the value given of 10,6TiB is too large; it could be
seen as 2,6TiB but not 0,6TiB (<=1932563136KiB) so we could presume that
a size below 4TiB would not be truncated which the 4th example confirms.

I do not know what is the maximum size accepted by md for a component,
but if the truncation happens outside mdadm (e.g. in the kernel), at
least a check should be added to mdadm.

The limit of 4TiB is the one of a 32bit address of sectors of 1KiB; I
cannot test this bug on a 64 bit platform.

-- System Information:
Debian Release: 8.7

bug reported on another computer; here is some manual info:

kernel debian linux-image-3.16.0-4-686-pae 3.16.36-1+deb8u2
processor AMD Athlon 32bit mono core