md: fix bug in handling of new_data_offset

commit c6563a8c38fde3c1c7fc925a10bde3ca20799301
    md: add possibility to change data-offset for devices.

introduced a 'new_data_offset' attribute which should normally
be the same as 'data_offset', but can be explicitly set to a different
value to allow a reshape operation to move the data.

Unfortunately when the 'data_offset' is explicitly set through
sysfs, the new_data_offset is not also set, so the two would become
out-of-sync incorrectly.

One result of this is that trying to set the 'size' after the
'data_offset' would fail because it is not permitted to set the size
when the 'data_offset' and 'new_data_offset' are different - as that
can be confusing.
Consequently when mdadm tried to do this while assembling an IMSM
array it would fail.

This bug was introduced in 3.5-rc1.

Reported-by: Brian Downing <bdowning@lavos.net>
Bisected-by: Brian Downing <bdowning@lavos.net>
Tested-by: Brian Downing <bdowning@lavos.net>
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/drivers/md/md.c b/drivers/md/md.c
index a4c219e3c859624925125e54029aac2da6211674..0c1fe4cbce6b2e3c823c963c3fb56aa2315d70c4 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -2931,6 +2931,7 @@ offset_store(struct md_rdev *rdev, const char *buf, size_t len)
                 * can be sane */
                return -EBUSY;
        rdev->data_offset = offset;
+       rdev->new_data_offset = offset;
        return len;
 }