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

From: Hannes Reinecke <hare@suse.de>
To: Christoph Hellwig <hch@lst.de>
Cc: "Jens Axboe" <axboe@kernel.dk>,
	"Justin Sanders" <justin@coraid.com>,
	"Josef Bacik" <josef@toxicpanda.com>,
	"Ilya Dryomov" <idryomov@gmail.com>,
	"Jack Wang" <jinpu.wang@cloud.ionos.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	"Jason Wang" <jasowang@redhat.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Stefan Hajnoczi" <stefanha@redhat.com>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>,
	"Minchan Kim" <minchan@kernel.org>,
	"Mike Snitzer" <snitzer@redhat.com>, "Song Liu" <song@kernel.org>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	dm-devel@redhat.com, linux-block@vger.kernel.org,
	drbd-dev@lists.linbit.com, nbd@other.debian.org,
	ceph-devel@vger.kernel.org, xen-devel@lists.xenproject.org,
	linux-raid@vger.kernel.org, linux-nvme@lists.infradead.org,
	linux-scsi@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 03/24] nvme: let set_capacity_revalidate_and_notify update the bdev size
Date: Mon, 9 Nov 2020 10:25:22 +0100	[thread overview]
Message-ID: <e79f9a96-ef53-d6ea-f6e7-e141bdd2e2d2@suse.de> (raw)
In-Reply-To: <20201109085340.GB27483@lst.de>

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@suse.de                              +49 911 74053 688
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