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

[Hannes Reinecke <hare@xxxxxxx>]

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
hare@xxxxxxx                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer