[PATCH 4.9 066/101] md: fix two problems with setting the "re-add" device state.

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: NeilBrown <neilb@xxxxxxxx>

commit 011abdc9df559ec75779bb7c53a744c69b2a94c6 upstream.

If "re-add" is written to the "state" file for a device
which is faulty, this has an effect similar to removing
and re-adding the device.  It should take up the
same slot in the array that it previously had, and
an accelerated (e.g. bitmap-based) rebuild should happen.

The slot that "it previously had" is determined by
rdev->saved_raid_disk.
However this is not set when a device fails (only when a device
is added), and it is cleared when resync completes.
This means that "re-add" will normally work once, but may not work a
second time.

This patch includes two fixes.
1/ when a device fails, record the ->raid_disk value in
    ->saved_raid_disk before clearing ->raid_disk
2/ when "re-add" is written to a device for which
    ->saved_raid_disk is not set, fail.

I think this is suitable for stable as it can
cause re-adding a device to be forced to do a full
resync which takes a lot longer and so puts data at
more risk.

Cc: <stable@xxxxxxxxxxxxxxx> (v4.1)
Fixes: 97f6cd39da22 ("md-cluster: re-add capabilities")
Signed-off-by: NeilBrown <neilb@xxxxxxxx>
Reviewed-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
Signed-off-by: Shaohua Li <shli@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/md/md.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -2694,7 +2694,8 @@ state_store(struct md_rdev *rdev, const
 			err = 0;
 		}
 	} else if (cmd_match(buf, "re-add")) {
-		if (test_bit(Faulty, &rdev->flags) && (rdev->raid_disk == -1)) {
+		if (test_bit(Faulty, &rdev->flags) && (rdev->raid_disk == -1) &&
+			rdev->saved_raid_disk >= 0) {
 			/* clear_bit is performed _after_ all the devices
 			 * have their local Faulty bit cleared. If any writes
 			 * happen in the meantime in the local node, they
@@ -8272,6 +8273,7 @@ static int remove_and_add_spares(struct
 			if (mddev->pers->hot_remove_disk(
 				    mddev, rdev) == 0) {
 				sysfs_unlink_rdev(mddev, rdev);
+				rdev->saved_raid_disk = rdev->raid_disk;
 				rdev->raid_disk = -1;
 				removed++;
 			}