Re: [PATCH v2] md: no longer compare spare disk superblock events in super_load

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Sep 25, 2019 at 01:54:49PM +0800, Yufen Yu wrote:
> We have a test case as follow:
> 
>   mdadm -CR /dev/md1 -l 1 -n 4 /dev/sd[a-d] --assume-clean --bitmap=internal
>   mdadm -S /dev/md1
>   mdadm -A /dev/md1 /dev/sd[b-c] --run --force
> 
>   mdadm --zero /dev/sda
>   mdadm /dev/md1 -a /dev/sda
> 
>   echo offline > /sys/block/sdc/device/state
>   echo offline > /sys/block/sdb/device/state
>   sleep 5
>   mdadm -S /dev/md1
> 
>   echo running > /sys/block/sdb/device/state
>   echo running > /sys/block/sdc/device/state
>   mdadm -A /dev/md1 /dev/sd[a-c] --run --force
> 
> When we readd /dev/sda to the array, it started to do recovery.
> After offline the other two disks in md1, the recovery have
> been interrupted and superblock update info cannot be written
> to the offline disks. While the spare disk (/dev/sda) can continue
> to update superblock info.
> 
> After stopping the array and assemble it, we found the array
> run fail, with the follow kernel message:
> 
> [  172.986064] md: kicking non-fresh sdb from array!
> [  173.004210] md: kicking non-fresh sdc from array!
> [  173.022383] md/raid1:md1: active with 0 out of 4 mirrors
> [  173.022406] md1: failed to create bitmap (-5)
> [  173.023466] md: md1 stopped.
> 
> Since both sdb and sdc have the value of 'sb->events' smaller than
> that in sda, they have been kicked from the array. However, the only
> remained disk sda is in 'spare' state before stop and it cannot be
> added to conf->mirrors[] array. In the end, raid array assemble and run fail.
> 
> In fact, we can use the older disk sdb or sdc to assemble the array.
> That means we should not choose the 'spare' disk as the fresh disk in
> analyze_sbs().
> 
> To fix the problem, we do not compare superblock events when it is
> a spare disk, as same as validate_super.
> 
> Signed-off-by: Yufen Yu <yuyufen@huawei.com>
> 
> v1->v2:
>   fix wrong return value in super_90_load
> ---
>  drivers/md/md.c | 44 ++++++++++++++++++++++++--------------------
>  1 file changed, 24 insertions(+), 20 deletions(-)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>