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From: Dan Williams <dan.j.williams@intel.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: linux-cxl@vger.kernel.org, "Weiny, Ira" <ira.weiny@intel.com>,
	Vishal L Verma <vishal.l.verma@intel.com>,
	"Schofield, Alison" <alison.schofield@intel.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/4] cxl/mem: Fix cdev_device_add() error handling
Date: Mon, 29 Mar 2021 21:48:44 -0700	[thread overview]
Message-ID: <CAPcyv4htAdJwAyGjeo+nxZNCOz5-zosCXxp2rwttxjfgxMK8uw@mail.gmail.com> (raw)
In-Reply-To: <20210329224439.GI2356281@nvidia.com>

On Mon, Mar 29, 2021 at 3:44 PM Jason Gunthorpe <jgg@nvidia.com> wrote:
>
> On Mon, Mar 29, 2021 at 02:03:37PM -0700, Dan Williams wrote:
>
> > Ugh, exactly why I was motivated to attempt to preclude this with new
> > core infrastructure that attempted to fix this centrally [1]. Remove
> > the  possibility of "others" getting this wrong. However after my
> > initial idea bounced off Greg then I ended up shipping this bug in the
> > local rewrite. I think the debugfs api gets this right in terms of
> > centralizing the reference count management, and I want to see
> > something similar for common driver ioctl patterns.
>
> There is a lot of variety here, I'm not sure how much valuable common
> code there will be that could be lifted into the core.. srcu,
> refcount, rwsem, percpu_ref, etc are all common implementations with
> various properties.
>
> The easist implementation is to just block driver destruction with a
> refcount & completion pattern
>
> The hardest is to allow the underlying HW driver to be removed from
> the fops while the file remains open.
>
> Usually whatever scheme is used has to flow into some in-kernel API as
> well, so isolating it in cdev may no be entirely helpful.
>
> The easisted helper API would be to add an 'unregistration lock' to
> the struct device that blocks unregistration. A refcount & completion
> for instance. I've seen that open coded enough times.

I do agree there is too much variety to widely unify. At the same time
it is a common enough pattern for devices that allow removal before
final close, especially devices that support hot-removal disconnecting
is a better pattern than blocking unregisteration.

Just the small matter of time to see this through...

  reply	other threads:[~2021-03-30  4:49 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-24 21:01 [PATCH 0/4] cxl/mem: Fix memdev device setup Dan Williams
2021-03-24 21:01 ` [PATCH 1/4] cxl/mem: Use sysfs_emit() for attribute show routines Dan Williams
2021-03-25 16:49   ` Jason Gunthorpe
2021-03-24 21:01 ` [PATCH 2/4] cxl/mem: Fix cdev_device_add() error handling Dan Williams
2021-03-25 17:11   ` Jason Gunthorpe
2021-03-29 21:03     ` Dan Williams
2021-03-29 22:44       ` Jason Gunthorpe
2021-03-30  4:48         ` Dan Williams [this message]
2021-03-24 21:02 ` [PATCH 3/4] cxl/mem: Do not rely on device_add() side effects for dev_set_name() failures Dan Williams
2021-03-25 17:14   ` Jason Gunthorpe
2021-03-24 21:02 ` [PATCH 4/4] cxl/mem: Disable cxl device power management Dan Williams

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