linux-kernel - [103/117] md: restore ability of spare drives to spin down.

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Message-Id: <20100510223326.682389596@kvm.kroah.org>
Date:	Mon, 10 May 2010 15:33:14 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	NeilBrown <neilb@...e.de>
Subject: [103/117] md: restore ability of spare drives to spin down.

2.6.33-stable review patch.  If anyone has any objections, please let us know.

------------------

From: NeilBrown <neilb@...e.de>

commit 1176568de7e066c0be9e46c37503b9fd4730edcf upstream.

Some time ago we stopped the clean/active metadata updates
from being written to a 'spare' device in most cases so that
it could spin down and say spun down.  Device failure/removal
etc are still recorded on spares.

However commit 51d5668cb2e3fd1827a55 broke this 50% of the time,
depending on whether the event count is even or odd.
The change log entry said:

   This means that the alignment between 'odd/even' and
    'clean/dirty' might take a little longer to attain,

how ever the code makes no attempt to create that alignment, so it
could take arbitrarily long.

So when we find that clean/dirty is not aligned with odd/even,
force a second metadata-update immediately.  There are already cases
where a second metadata-update is needed immediately (e.g. when a
device fails during the metadata update).  We just piggy-back on that.

Reported-by: Joe Bryant <tenminjoe@...oo.com>
Signed-off-by: NeilBrown <neilb@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/md/md.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -2108,12 +2108,18 @@ repeat:
 		if (!mddev->in_sync || mddev->recovery_cp != MaxSector) { /* not clean */
 			/* .. if the array isn't clean, an 'even' event must also go
 			 * to spares. */
-			if ((mddev->events&1)==0)
+			if ((mddev->events&1)==0) {
 				nospares = 0;
+				sync_req = 2; /* force a second update to get the
+					       * even/odd in sync */
+			}
 		} else {
 			/* otherwise an 'odd' event must go to spares */
-			if ((mddev->events&1))
+			if ((mddev->events&1)) {
 				nospares = 0;
+				sync_req = 2; /* force a second update to get the
+					       * even/odd in sync */
+			}
 		}
 	}

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