linux-kernel - Re: [RFC PATCH 0/3] gpu: nova-core: add basic timer subdevice implementation

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Message-Id: <D82UB3V6NZ55.3OEPPW2W8MFZV@nvidia.com>
Date: Wed, 26 Feb 2025 17:34:01 -0800
From: "John Hubbard" <jhubbard@...dia.com>
To: "Greg KH" <gregkh@...uxfoundation.org>, "Jason Gunthorpe"
 <jgg@...dia.com>
Cc: "Danilo Krummrich" <dakr@...nel.org>, "Joel Fernandes"
 <joelagnelf@...dia.com>, "Alexandre Courbot" <acourbot@...dia.com>, "Dave
 Airlie" <airlied@...il.com>, "Gary Guo" <gary@...yguo.net>, "Joel
 Fernandes" <joel@...lfernandes.org>, "Boqun Feng" <boqun.feng@...il.com>,
 "Ben Skeggs" <bskeggs@...dia.com>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>, <nouveau@...ts.freedesktop.org>,
 <dri-devel@...ts.freedesktop.org>, <paulmck@...nel.org>
Subject: Re: [RFC PATCH 0/3] gpu: nova-core: add basic timer subdevice
 implementation

On Wed Feb 26, 2025 at 5:02 PM PST, Greg KH wrote:
> On Wed, Feb 26, 2025 at 07:47:30PM -0400, Jason Gunthorpe wrote:
>> The way misc device works you can't unload the module until all the
>> FDs are closed and the misc code directly handles races with opening
>> new FDs while modules are unloading. It is quite a different scheme
>> than discussed in this thread.
>
> And I would argue that is it the _right_ scheme to be following overall
> here.  Removing modules with in-flight devices/drivers is to me is odd,
> and only good for developers doing work, not for real systems, right?

Right...I think. I'm not experienced with misc, but I do know that the
"run driver code after driver release" is very, very concerning.

I'm quite new to drivers/gpu/drm, so this is the first time I've learned
about this DRM behavior...

>
> Yes, networking did add that functionality to allow modules to be
> unloaded with network connections open, and I'm guessing RDMA followed
> that, but really, why?
>
> What is the requirement that means that you have to do this for function
> pointers?  I can understand the disconnect issue between devices and
> drivers and open file handles (or sockets), as that is a normal thing,
> but not removing code from the system, that is not normal.
>

I really hope that this "run after release" is something that Rust for
Linux drivers, and in particular, the gpu/nova*, gpu/drm/nova* drivers,
can *leave behind*.

DRM may have had ${reasons} for this approach, but this nova effort is
rebuilding from the ground up. So we should avoid just blindly following
this aspect of the original DRM design.

thanks,
--
John Hubbard