Re: [PATCH 03/24] nvme: let set_capacity_revalidate_and_notify update the bdev size

Hannes Reinecke
2020-11-09T09:25:35Z

On 11/9/20 9:53 AM, Christoph Hellwig wrote:
> On Mon, Nov 09, 2020 at 08:53:58AM +0100, Hannes Reinecke wrote:
>>> index 376096bfc54a83..4e86c9aafd88a7 100644
>>> --- a/drivers/nvme/host/core.c
>>> +++ b/drivers/nvme/host/core.c
>>> @@ -2053,7 +2053,7 @@ static void nvme_update_disk_info(struct gendisk *disk,
>>> capacity = 0;
[ .. ]
>> Originally nvme multipath would update/change the size of the multipath
>> device according to the underlying path devices.
>> With this patch the size of the multipath device will _not_ change if there
>> is a change on the underlying devices.
>
> Yes, it will. Take a close look at nvme_update_disk_info and how it is
> called.
>
Okay, then: What would be the correct way of handling a size update for
NVMe multipath?
Assuming we're getting an AEN for each path signalling the size change
(or a controller reset leading to a size change).
So if we're updating the size of the multipath device together with the
path device at the first AEN/reset we'll end up with the other paths
having a different size than the multipath device (and the path we've
just been updating).
- Do we care, or cross fingers and hope for the best?
- Shouldn't we detect the case where we won't get a size update for the
other paths, or, indeed, we have a genuine device size mismatch due to a
misconfiguration on the target?

IE shouldn't we have a flag 'size update pending' for the other paths,,
to take them out ouf use temporarily until the other AENs/resets have
been processed?

Cheers,

Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
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