Re: [PATCH 01/24] rust: driver core: drop drvdata before devres release

[Alice Ryhl <aliceryhl@google.com>]

On Tue, Apr 28, 2026 at 12:10:59AM +0200, Danilo Krummrich wrote:
> Move the post_unbind_rust callback before devres_release_all() in
> device_unbind_cleanup().
> 
> With drvdata() removed, the driver's bus device private data is only
> accessible by the owning driver itself. It is hence safe to drop the
> driver's bus device private data before devres actions are released.
> 
> This reordering is the key enabler for Higher-Ranked Lifetime Types
> (HRT) in Rust device drivers -- it allows driver structs to hold direct
> references to devres-managed resources, because the bus device private
> data (and with it all such references) is guaranteed to be dropped while
> the underlying devres resources are still alive.
> 
> Without this change, devres resources would be freed first, leaving the
> driver's bus device private data with dangling references during its
> destructor.
> 
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> ---
>  drivers/base/dd.c             | 2 +-
>  include/linux/device/driver.h | 4 ++--
>  rust/kernel/driver.rs         | 4 ++--
>  3 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 5799a60fd058..be59d2e13a15 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -593,9 +593,9 @@ static DEVICE_ATTR_RW(state_synced);
>  
>  static void device_unbind_cleanup(struct device *dev)
>  {
> -	devres_release_all(dev);
>  	if (dev->driver->p_cb.post_unbind_rust)
>  		dev->driver->p_cb.post_unbind_rust(dev);
> +	devres_release_all(dev);
>  	arch_teardown_dma_ops(dev);
>  	kfree(dev->dma_range_map);
>  	dev->dma_range_map = NULL;

I seem to recall that we discussed a plan to have two classes of devres
callbacks where device unbind proceeds as follows:

1. Run first class of devres callbacks.
2. Device is now considered unbound.
3. Run second class of devres callbacks.

Is that still the plan?

Alice