Re: [PATCH V3 0/3] Ensure ordered namespace registration during async scan

[Hannes Reinecke <hare@suse.de>]

On 6/19/26 20:45, Keith Busch wrote:
> On Fri, Jun 19, 2026 at 07:59:43AM +0200, Hannes Reinecke wrote:
>> The problem here is namespace lifetime. The ns_ida is only ever released
>> at the very last step, so the 'number' of the namespace will only be freed
>> once all references to the namespace are dropped.
>> So if you were trying to keep the namespace number ordered you would
>> have to delay the creation of the namespace until that point, and you
>> would induce a serialization between deletion and creation.
> 
> Under the proposed scheme, there is no ns_ida. You just use the NSID of
> the namespace, and that's it. You have to ensure that del_gendisk
> completed on all heads and paths that was using it prior to bringing up
> the next one, but that's not really a problem.
> 
But then you'll have to delay the (re-)scan until the very last 
reference is gone, otherwise the nsid the scan is about to create
will be blocked by the nsid still pending to be deleted.

And we do have blktest nvme/058 as a really nice testcase for executing
rapid namespace remapping; that regularly manages to get the 'nsid'
and 'ns_ida' numbers getting out of sync.

In general I fail to see the issue here.
Any modern distro should be using persistent device links to access
devices, so the actual device name is pretty much irrelevant.
We on our side haven't had any issues here since ages.

And scanning has been one of the most complex operations we are doing
on nvme, and so I'd really think twice before changing that.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@suse.de                                +49 911 74053 688
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