Re: [PATCH v2 1/2] rust: add abstraction for struct device

Greg KH
2024-06-12T15:02:54Z

On Wed, Jun 12, 2024 at 04:51:42PM +0200, Danilo Krummrich wrote:
> On 6/11/24 18:13, Boqun Feng wrote:
> > On Tue, Jun 11, 2024 at 03:29:22PM +0200, Greg KH wrote:
> > > On Tue, Jun 11, 2024 at 03:21:31PM +0200, Danilo Krummrich wrote:
> > > > ...hence, I agree we should indeed add to the #Invariants and #Safety section
> > > > that `->release` must be callable from any thread.
> > > >
> > > > However, this is just theory, do we actually have cases where `device::release`
> >
> > @Danilo, right, it's only theorical, but it's good to call it out since
> > it's the requirement for a safe Rust abstraction.
>
> Similar to my previous reply, if we want to call this out as safety requirement
> in `Device::from_raw`, we probably want to add it to the documentation of the C
> `struct device`, such that we can argue that this is an invariant of C's
> `struct device`.
>
> Otherwise we'd have to write something like:
>
> "It must also be ensured that the `->release` function of a `struct device` can
> be called from any non-atomic context. While not being officially documented this
> is guaranteed by the invariant of `struct device`."

In the 20+ years of the driver model being part of the kernel, I don't
think this has come up yet, so maybe you can call the release function
in irq context. I don't know, I was just guessing :)

So let's not go adding constraints that we just do not have please.
Same goes for the C code, so the rust code is no different here.

thanks,

greg k-h