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Subject[34-longterm 175/209] md: fix bug with re-adding of partially recovered device.
From: NeilBrown <>

| This is a commit scheduled for the next v2.6.34 longterm release. |
| If you see a problem with using this for longterm, please comment.|

commit 1a855a0606653d2d82506281e2c686bacb4b2f45 upstream.

With v0.90 metadata, a hot-spare does not become a full member of the
array until recovery is complete. So if we re-add such a device to
the array, we know that all of it is as up-to-date as the event count
would suggest, and so it a bitmap-based recovery is possible.

However with v1.x metadata, the hot-spare immediately becomes a full
member of the array, but it record how much of the device has been
recovered. If the array is stopped and re-assembled recovery starts
from this point.

When such a device is hot-added to an array we currently lose the 'how
much is recovered' information and incorrectly included it as a full
in-sync member (after bitmap-based fixup).
This is wrong and unsafe and could corrupt data.

So be more careful about setting saved_raid_disk - which is what
guides the re-adding of devices back into an array.
The new code matches the code in slot_store which does a similar
thing, which is encouraging.

This is suitable for any -stable kernel.

Reported-by: "Dailey, Nate" <>
Signed-off-by: NeilBrown <>
Signed-off-by: Paul Gortmaker <>
drivers/md/md.c | 7 +++++--
1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 92dbef5..cf511de 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5008,7 +5008,7 @@ static int add_new_disk(mddev_t * mddev, mdu_disk_info_t *info)
return PTR_ERR(rdev);
- /* set save_raid_disk if appropriate */
+ /* set saved_raid_disk if appropriate */
if (!mddev->persistent) {
if (info->state & (1<<MD_DISK_SYNC) &&
info->raid_disk < mddev->raid_disks)
@@ -5018,7 +5018,10 @@ static int add_new_disk(mddev_t * mddev, mdu_disk_info_t *info)
} else
validate_super(mddev, rdev);
- rdev->saved_raid_disk = rdev->raid_disk;
+ if (test_bit(In_sync, &rdev->flags))
+ rdev->saved_raid_disk = rdev->raid_disk;
+ else
+ rdev->saved_raid_disk = -1;

clear_bit(In_sync, &rdev->flags); /* just to be sure */
if (info->state & (1<<MD_DISK_WRITEMOSTLY))

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