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SubjectPULL REQUEST - serious md/RAID10 bug in 3.1 when activating a hot-spare.

Hi Linus et al,

I just discovered a fairly serious flaw that I introduced into 3.1 - details

Anyone running RAID10 with 3.1 is advised to either apply this patch or
revert an earlier kernel as soon as possible. In the mean time, remove any
hot spares from an RAID10 array.


The following changes since commit d890fa2b0586b6177b119643ff66932127d58afa:

md: Fix some bugs in recovery_disabled handling. (2011-10-26 11:54:39 +1100)

are available in the git repository at:
git:// for-linus

last commit being 7fcc7c8acf0fba44d19a713207af7e58267c1179

NeilBrown (1):
md/raid10: Fix bug when activating a hot-spare.

drivers/md/raid10.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

commit 7fcc7c8acf0fba44d19a713207af7e58267c1179
Author: NeilBrown <>
Date: Mon Oct 31 12:59:44 2011 +1100

md/raid10: Fix bug when activating a hot-spare.

This is a fairly serious bug in RAID10.

When a RAID10 array is degraded and a hot-spare is activated, the
spare does not take up the empty slot, but rather replaces the first
working device.
This is likely to make the array non-functional. It would normally
be possible to recover the data, but that would need care and is not

This bug was introduced in commit
which first appeared in 3.1.

Signed-off-by: NeilBrown <>

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 132c18e..c025a82 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1355,7 +1355,7 @@ static int raid10_add_disk(struct mddev *mddev, struct md_rdev *rdev)
struct mirror_info *p = &conf->mirrors[mirror];
if (p->recovery_disabled == mddev->recovery_disabled)
- if (!p->rdev)
+ if (p->rdev)

disk_stack_limits(mddev->gendisk, rdev->bdev,[unhandled content-type:application/pgp-signature]
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