[PATCH] md: make sure 64bit fields in version-1 metadata are 64-bit aligned

reshape_position is a 64bit field that was not 64bit aligned.  So swap with
new_level.

NOTE: this is a user-visible change.  However:
  - The bad code has not appeared in a released kernel
  - This code is still marked 'experimental'
  - This only affects version-1 superblock, which are not in wide use
  - These field are only used (rather than simply reported) by user-space
    tools in extemely rare circumstances : after a reshape crashes in the
    first second of the reshape process.

So I believe that, at this stage, the change is safe.  Especially if people
heed the 'help' message on use mdadm-2.4.1.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 7 insertions, 6 deletions

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index fd2aae150ccc..ac25a48362ac 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -139,11 +139,12 @@ config MD_RAID5_RESHAPE
           is online.  However it is still EXPERIMENTAL code.  It should
           work, but please be sure that you have backups.
 
-          You will need a version of mdadm newer than 2.3.1.   During the
-          early stage of reshape there is a critical section where live data
-          is being over-written.  A crash during this time needs extra care
-          for recovery.  The newer mdadm takes a copy of the data in the
-          critical section and will restore it, if necessary, after a crash.
+          You will need mdadm verion 2.4.1 or later to use this
+          feature safely.  During the early stage of reshape there is
+          a critical section where live data is being over-written.  A
+          crash during this time needs extra care for recovery.  The
+          newer mdadm takes a copy of the data in the critical section
+          and will restore it, if necessary, after a crash.
 
           The mdadm usage is e.g.
                mdadm --grow /dev/md1 --raid-disks=6
diff --git a/include/linux/raid/md_p.h b/include/linux/raid/md_p.h
index 774e1acfb8c4..f1fbae7e390e 100644
--- a/include/linux/raid/md_p.h
+++ b/include/linux/raid/md_p.h
@@ -227,8 +227,8 @@ struct mdp_superblock_1 {
                                  */
 
         /* These are only valid with feature bit '4' */
-        __u64   reshape_position;       /* next address in array-space for reshape */
         __u32   new_level;      /* new level we are reshaping to                */
+        __u64   reshape_position;       /* next address in array-space for reshape */
         __u32   delta_disks;    /* change in number of raid_disks               */
         __u32   new_layout;     /* new layout                                   */
         __u32   new_chunk;      /* new chunk size (bytes)                       */