[PATCHv4] nvme: allow to re-attach namespaces after all paths are down

[Keith Busch]

On Mon, May 17, 2021 at 05:36:39PM +0200, Hannes Reinecke wrote:
> On 5/17/21 5:26 PM, Keith Busch wrote:
> > On Mon, May 17, 2021 at 10:18:09AM +0200, Hannes Reinecke wrote:
> >> We should only remove the ns head from the list of heads per
> >> subsystem if the reference count drops to zero. Removing it
> >> at the start of nvme_ns_remove() will prevent us from reattaching
> >> the namespace to the correct ns head once a path becomes available
> >> again.
> > 
> > This looks fine to me
> > 
> > Reviewed-by: Keith Busch <kbusch at kernel.org>
> > 
> > There are potential corner cases associated with namespace management
> > that can cause problems here, but it would certainly be a user error
> > that needs manual intervention anyway. I suspect those scenarios are
> > very uncommon too, so I think we can deal with that later if it becomes
> > a problem.
> > 
> How so?
> We're keeping a copy of the NS IDs around, so after reconnect the
> namespace would have to provide same set of NS IDs.
> 
> If the namespace is different yet providing the same NS IDs we'll have a
> problem even with the current code, as we're using the ND ID to identify
> multipathed namespaces.
> 
> Or do you have a different scenario in mind?

Sorry, I didn't mean to imply this creates a new problem. It's already a
problem. :)

This just provides a chance for a recycled ID for a newly created
namespace to attach to an in-use head associated with a previously
deleted namespace. I am not really concerned about this scenario,
though, since it wouldn't work today anyway.