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From: Keith Busch <kbusch@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Keith Busch <keith.busch@intel.com>,
	Hannes Reinecke <hare@suse.com>, Sagi Grimberg <sagi@grimberg.me>,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
	Jens Axboe <axboe@fb.com>, Logan Gunthorpe <logang@deltatee.com>
Subject: Re: [PATCH] nvme-core: Fix subsystem instance mismatches
Date: Wed, 4 Sep 2019 09:54:45 -0600	[thread overview]
Message-ID: <20190904155445.GD21302@localhost.localdomain> (raw)
In-Reply-To: <20190904154215.GA20422@lst.de>

On Wed, Sep 04, 2019 at 05:42:15PM +0200, Christoph Hellwig wrote:
> On Wed, Sep 04, 2019 at 08:44:27AM -0600, Keith Busch wrote:
> > Let me step through an example:
> > 
> >   Ctrl A gets instance 0.
> > 
> >   Its subsystem gets the same instance, and takes ref count on it:
> >   all namespaces in this subsystem will use '0'.
> > 
> >   Ctrl B gets instance 1, and it's in the same subsystem as Ctrl A so
> >   no new subsytem is allocated.
> > 
> >   Ctrl A is disconnected, dropping its ref on instance 0, but the
> >   subsystem still has its refcount, making it unavailable.
> > 
> >   Ctrl A is reconnected, and allocates instance 2 because 0 is still in
> >   use.
> > 
> > Now all the namespaces in this subsystem are prefixed with nvme0, but no
> > controller exists with the same prefix. We still have inevitable naming
> > mismatch, right?
> 
> I think th major confusion was that we can use the same handle for
> and unrelated subsystem vs controller, and that would avoid it.
>
> I don't see how we can avoid the controller is entirely different
> from namespace problem ever.

Can we just ensure there is never a matching controller then? This
patch will accomplish that and simpler than wrapping the instance in a
refcount'ed object:

http://lists.infradead.org/pipermail/linux-nvme/2019-May/024142.html

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WARNING: multiple messages have this Message-ID (diff)
From: Keith Busch <kbusch@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@fb.com>, Hannes Reinecke <hare@suse.com>,
	Sagi Grimberg <sagi@grimberg.me>,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
	Keith Busch <keith.busch@intel.com>,
	Logan Gunthorpe <logang@deltatee.com>
Subject: Re: [PATCH] nvme-core: Fix subsystem instance mismatches
Date: Wed, 4 Sep 2019 09:54:45 -0600	[thread overview]
Message-ID: <20190904155445.GD21302@localhost.localdomain> (raw)
In-Reply-To: <20190904154215.GA20422@lst.de>

On Wed, Sep 04, 2019 at 05:42:15PM +0200, Christoph Hellwig wrote:
> On Wed, Sep 04, 2019 at 08:44:27AM -0600, Keith Busch wrote:
> > Let me step through an example:
> > 
> >   Ctrl A gets instance 0.
> > 
> >   Its subsystem gets the same instance, and takes ref count on it:
> >   all namespaces in this subsystem will use '0'.
> > 
> >   Ctrl B gets instance 1, and it's in the same subsystem as Ctrl A so
> >   no new subsytem is allocated.
> > 
> >   Ctrl A is disconnected, dropping its ref on instance 0, but the
> >   subsystem still has its refcount, making it unavailable.
> > 
> >   Ctrl A is reconnected, and allocates instance 2 because 0 is still in
> >   use.
> > 
> > Now all the namespaces in this subsystem are prefixed with nvme0, but no
> > controller exists with the same prefix. We still have inevitable naming
> > mismatch, right?
> 
> I think th major confusion was that we can use the same handle for
> and unrelated subsystem vs controller, and that would avoid it.
>
> I don't see how we can avoid the controller is entirely different
> from namespace problem ever.

Can we just ensure there is never a matching controller then? This
patch will accomplish that and simpler than wrapping the instance in a
refcount'ed object:

http://lists.infradead.org/pipermail/linux-nvme/2019-May/024142.html

  reply	other threads:[~2019-09-04 15:56 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-31  0:01 [PATCH] nvme-core: Fix subsystem instance mismatches Logan Gunthorpe
2019-08-31  0:01 ` Logan Gunthorpe
2019-08-31 15:29 ` Keith Busch
2019-08-31 15:29   ` Keith Busch
2019-09-03 16:08   ` Logan Gunthorpe
2019-09-03 16:08     ` Logan Gunthorpe
2019-09-03 16:46     ` Keith Busch
2019-09-03 16:46       ` Keith Busch
2019-09-03 18:13       ` Logan Gunthorpe
2019-09-03 18:13         ` Logan Gunthorpe
2019-09-04  6:05       ` Christoph Hellwig
2019-09-04  6:05         ` Christoph Hellwig
2019-09-04 14:44         ` Keith Busch
2019-09-04 14:44           ` Keith Busch
2019-09-04 15:42           ` Christoph Hellwig
2019-09-04 15:42             ` Christoph Hellwig
2019-09-04 15:54             ` Keith Busch [this message]
2019-09-04 15:54               ` Keith Busch
2019-09-04 16:02               ` Christoph Hellwig
2019-09-04 16:02                 ` Christoph Hellwig
2019-09-04 16:07               ` Logan Gunthorpe
2019-09-04 16:07                 ` Logan Gunthorpe
2019-09-04 16:35                 ` Keith Busch
2019-09-04 16:35                   ` Keith Busch
2019-09-04 17:01                   ` Logan Gunthorpe
2019-09-04 17:01                     ` Logan Gunthorpe
2019-09-04 17:14                     ` Keith Busch
2019-09-04 17:14                       ` Keith Busch
2019-09-04 17:29                       ` Logan Gunthorpe
2019-09-04 17:29                         ` Logan Gunthorpe

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