[PATCHv2] nvme-mpath: delete disk after last connection

[Keith Busch]

On Tue, Apr 20, 2021 at 03:19:10PM +0200, Hannes Reinecke wrote:
> On 4/20/21 10:05 AM, Christoph Hellwig wrote:
> > On Fri, Apr 16, 2021 at 08:24:11AM +0200, Hannes Reinecke wrote:
> > > With the proposed patch, the following messages appear:
> > > 
> > >   [  227.516807] md/raid1:md0: Disk failure on nvme3n1, disabling device.
> > >   [  227.516807] md/raid1:md0: Operation continuing on 1 devices.
> > 
> > So how is this going to work for e.g. a case where the device
> > disappear due to resets or fabrics connection problems?  This now
> > directly teards down the device.
> > 
> Yes, that is correct; the nshead will be removed once the last path is
> _removed_.

The end result is also how non-multipath nvme behaves, so I think that's
what users have come to expect.

> But key point here is that once the system finds itself in that
> situation it's impossible to recover, as the refcounts are messed.
> Even a manual connect call with the same parameter will _not_ restore
> operation, but rather result in a new namespace.

I haven't looked at this yet, but is it really not possible to restore
the original namespace upon the reestablished connection?

> So with this patch we change from stalled I/O (where the user has to
> reboot the machine to restore operation) to I/O errors (giving the user at
> least a _chance_ to recover).
> 
> I can easily consider adding a 'queue_if_no_path' option to allow I/O to be
> held even once all paths are disconnected, but that will be enother patch.