[3.16.y-ckt stable] Patch "md/raid10: always set reshape_safe when initializing reshape_position." has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    md/raid10: always set reshape_safe when initializing reshape_position.

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt18.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From cfeea5fd8a50696804adab236c312a7159edd00b Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb at suse.com>
Date: Mon, 6 Jul 2015 17:37:49 +1000
Subject: md/raid10: always set reshape_safe when initializing
 reshape_position.

commit 299b0685e31c9f3dcc2d58ee3beca761a40b44b3 upstream.

'reshape_position' tracks where in the reshape we have reached.
'reshape_safe' tracks where in the reshape we have safely recorded
in the metadata.

These are compared to determine when to update the metadata.
So it is important that reshape_safe is initialised properly.
Currently it isn't.  When starting a reshape from the beginning
it usually has the correct value by luck.  But when reducing the
number of devices in a RAID10, it has the wrong value and this leads
to the metadata not being updated correctly.
This can lead to corruption if the reshape is not allowed to complete.

This patch is suitable for any -stable kernel which supports RAID10
reshape, which is 3.5 and later.

Fixes: 3ea7daa5d7fd ("md/raid10: add reshape support")
Signed-off-by: NeilBrown <neilb at suse.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/md/raid10.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index a46124ecafc7..73c9f579b042 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -3585,6 +3585,7 @@ static struct r10conf *setup_conf(struct mddev *mddev)
 			/* far_copies must be 1 */
 			conf->prev.stride = conf->dev_sectors;
 	}
+	conf->reshape_safe = conf->reshape_progress;
 	spin_lock_init(&conf->device_lock);
 	INIT_LIST_HEAD(&conf->retry_list);

@@ -3793,7 +3794,6 @@ static int run(struct mddev *mddev)
 		}
 		conf->offset_diff = min_offset_diff;

-		conf->reshape_safe = conf->reshape_progress;
 		clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
 		clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
 		set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
@@ -4138,6 +4138,7 @@ static int raid10_start_reshape(struct mddev *mddev)
 		conf->reshape_progress = size;
 	} else
 		conf->reshape_progress = 0;
+	conf->reshape_safe = conf->reshape_progress;
 	spin_unlock_irq(&conf->device_lock);

 	if (mddev->delta_disks && mddev->bitmap) {
@@ -4204,6 +4205,7 @@ abort:
 		rdev->new_data_offset = rdev->data_offset;
 	smp_wmb();
 	conf->reshape_progress = MaxSector;
+	conf->reshape_safe = MaxSector;
 	mddev->reshape_position = MaxSector;
 	spin_unlock_irq(&conf->device_lock);
 	return ret;
@@ -4556,6 +4558,7 @@ static void end_reshape(struct r10conf *conf)
 	md_finish_reshape(conf->mddev);
 	smp_wmb();
 	conf->reshape_progress = MaxSector;
+	conf->reshape_safe = MaxSector;
 	spin_unlock_irq(&conf->device_lock);

 	/* read-ahead size must cover two whole stripes, which is