Re: [PATCH] mdadm reshape hangs on external grow chunk

[Kinga Tanska <kinga.tanska@linux.intel.com>]

On Fri, 23 Sep 2022 10:26:35 -0400
Nigel Croxon <ncroxon@redhat.com> wrote:

> After creating a raid array on top of a imsm container. Try to
> grow the chunk size and the reshape will hang with zero progress.
> The reason is the computation of sync_max_to_set value:
> if (before_data_disks <= data_disks)
>         sync_max_to_set = sra->reshape_progress / data_disks;
>     else
>         sync_max_to_set = (sra->component_size * data_disks
>                        - sra->reshape_progress) / data_disks;
> 
> Can produce a zero result. Which is then used to set the maximum
> sync value, causing zero progress to the reshape.  The change is to
> test if the sync_max_to_set value is zero. And if so, set the sysfs
> sync_max to "max".
> 
> Steps to Reproduce:
> 1. Create a container and RAID0 array
> mdadm -CR /dev/md/imsm -e imsm -n2 /dev/nvme0n1 /dev/nvme1n1
> mdadm -CR  /dev/md/vol -l0 --chunk=16 -n2 /dev/nvme0n1 /dev/nvme1n1
> 2. Wait for resync
> 3. Try to grow the chunk size
> mdadm --grow /dev/md/vol --chunk=256
> 
> Signed-off-by: Nigel Croxon <ncroxon@redhat.com>
> ---
>  Grow.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/Grow.c b/Grow.c
> index 0f07a894..6c5021bc 100644
> --- a/Grow.c
> +++ b/Grow.c
> @@ -943,7 +943,7 @@ int start_reshape(struct mdinfo *sra, int
> already_running, if (!already_running)
>  		sysfs_set_num(sra, NULL, "sync_min",
> sync_max_to_set); 
> -        if (st->ss->external)
> +        if (sync_max_to_set)
>  		err = err ?: sysfs_set_num(sra, NULL, "sync_max",
> sync_max_to_set); else
>  		err = err ?: sysfs_set_str(sra, NULL, "sync_max",
> "max");

Hi Nigel,

I was trying to retest with your patch but still have the defect. I
analyzed it and found another reason, which causes this defect. In
validate_geometry_imsm function freesize and super is being checked and
return 1 if any of those is NULL. In my opinion 0 shall be returned
here, because it is an error and reshape should be stopped here. I will
prepare proper patch and send to review immediately.

King regards,
Kinga Tanska