Re: [PATCH v8 3/5] rust: add basic serial device bus abstractions

[Danilo Krummrich]

On Sat May 30, 2026 at 6:23 PM CEST, Markus Probst wrote:
> On Sat, 2026-05-30 at 18:14 +0200, Danilo Krummrich wrote:
>> On Sat May 30, 2026 at 4:51 PM CEST, Markus Probst wrote:
>> > On Sat, 2026-05-30 at 16:35 +0200, Danilo Krummrich wrote:
>> > > On Sat May 30, 2026 at 4:27 PM CEST, Markus Probst wrote:
>> > > > This would work, but I don't see how it would get rid of rust_private_data in
>> > > > this way. The device private data will but the private bus abstraction data
>> > > > needs to outlive the devres callbacks (which is done by rust_private_data).
>> > > 
>> > > Why? You only ever use it in the receive callback, which won't be called after
>> > > device unbind anymore.
>> > Because the possibility exists that some classdev ops or Drop calls
>> > e.g. sdev.set_baudrate. This is a null pointer dereference after
>> > serdev_device_close has been called. I interpreted it to add a state to
>> > the abstraction private data which would prevent those calls (early
>> > return with error) after serdev_device_close has been called, but this
>> > would only work if it outlives these calls.
>> > 
>> > But it seems you were refering to something else with the state?
>> 
>> Yes, but I just notice that I'm a step ahead. With the lifetime model class
>> device registrations shouldn't be guarded with Devres anymore, but with a
>> lifetime.
>> 
>> (This also entirely eliminates the need for having different devres stages to
>> prevent drivers from smuggling a newly created Devres object into an existing
>> Devres<Registration<T>>'s data, which would be unsound for obvious reasons.)
>> 
>> With this there is no way there are still class device callbacks after the bus
>> device private data has been dropped in the first place.
> There would still be Drop, which can access the device.
> Drop happens after remove_callback.

But you control drop(), so can order it such that first the driver's bus device
private data drops and after this the private data of the bus wrapping it (which
will also call serdev_device_close()).

> Might be simpler for now: I can use a mutex to prevent calls in
> receive_buf after remove_callback has been called.
>
> Thanks
> - Markus Probst