Re: [PATCH] FIX: Cleanup after raid45->raid0 takeover

[NeilBrown <neilb@suse.de>]

On Mon, 28 Mar 2011 15:31:57 +0200 Krzysztof Wojcik
<krzysztof.wojcik@intel.com> wrote:

> Problem:
> After raid4->raid0 takeover operation, another takeover operation
> (e.g raid0->raid10) results "kernel oops".
> Root cause:
> Variables 'degraded' and 'plug' in mddev structure are not cleared
> after raid45->raid0 takeover.
> 
> This patch reset these variables.
> 
> Signed-off-by: Krzysztof Wojcik <krzysztof.wojcik@intel.com>
> ---
>  drivers/md/raid0.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
> index c0ac457..5d47113 100644
> --- a/drivers/md/raid0.c
> +++ b/drivers/md/raid0.c
> @@ -603,6 +603,8 @@ static void *raid0_takeover_raid45(mddev_t *mddev)
>  	mddev->new_chunk_sectors = mddev->chunk_sectors;
>  	mddev->raid_disks--;
>  	mddev->delta_disks = -1;
> +	mddev->degraded = 0;
> +	mddev->plug = NULL;
>  	/* make sure it will be not marked as dirty */
>  	mddev->recovery_cp = MaxSector;
>  

This is wrong.

The raid0 'takeover' method is called while the raid5 array is still active,
and mddev->plug and mddev->degraded are used by the active array.  So you
cannot just clear them like this.  The new_* and delta_disks values are not
used by an active array - also raid_disks isn't used - each personality keeps
a copy of the effective raid_disks in it's private structure.

So the ->plug must be cleared in the raid5 stop routine, and degraded
should be cleared by level_store after calling ->stop on the raid5 and before
calling ->run on the raid0.

I have changed the patch to do that instead.

Thanks,
NeilBrown