From: Danilo Krummrich Date: Fri, 13 Feb 2026 22:07:15 +0000 (+0100) Subject: rust: devres: embed struct devres_node directly X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9aa64d2503c6f5a803ff2990608312e5bdc6b0de;p=thirdparty%2Fkernel%2Flinux.git rust: devres: embed struct devres_node directly Currently, the Devres container uses devm_add_action() to register a devres callback. devm_add_action() allocates a struct action_devres, which on top of struct devres_node, just keeps a data pointer and release function pointer. This is an unnecessary indirection, given that analogous to struct devres, the Devres container can just embed a struct devres_node directly without an additional allocation. In contrast to struct devres, we don't need to force an alignment of ARCH_DMA_MINALIGN (as struct devres does to account for the worst case) since we have generics in Rust. I.e. the compiler already ensures correct alignment of the embedded T in Devres. Thus, get rid of devm_add_action() and instead embed a struct devres_node directly. Reviewed-by: Alice Ryhl Acked-by: Greg Kroah-Hartman Link: https://patch.msgid.link/20260213220718.82835-6-dakr@kernel.org [ * Improve comment about core::any::type_name(), * add #[must_use] to devres_node_remove(), * use container_of!() in devres_node_free_node(). - Danilo ] Signed-off-by: Danilo Krummrich --- diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs index 6afe196be42c2..9e5f93aed20cf 100644 --- a/rust/kernel/devres.rs +++ b/rust/kernel/devres.rs @@ -23,9 +23,22 @@ use crate::{ rcu, Arc, // }, - types::ForeignOwnable, + types::{ + ForeignOwnable, + Opaque, // + }, }; +/// Inner type that embeds a `struct devres_node` and the `Revocable`. +#[repr(C)] +#[pin_data] +struct Inner { + #[pin] + node: Opaque, + #[pin] + data: Revocable, +} + /// This abstraction is meant to be used by subsystems to containerize [`Device`] bound resources to /// manage their lifetime. /// @@ -111,12 +124,64 @@ use crate::{ /// ``` pub struct Devres { dev: ARef, - /// Pointer to [`Self::devres_callback`]. - /// - /// Has to be stored, since Rust does not guarantee to always return the same address for a - /// function. However, the C API uses the address as a key. - callback: unsafe extern "C" fn(*mut c_void), - data: Arc>, + inner: Arc>, +} + +// Calling the FFI functions from the `base` module directly from the `Devres` impl may result in +// them being called directly from driver modules. This happens since the Rust compiler will use +// monomorphisation, so it might happen that functions are instantiated within the calling driver +// module. For now, work around this with `#[inline(never)]` helpers. +// +// TODO: Remove once a more generic solution has been implemented. For instance, we may be able to +// leverage `bindgen` to take care of this depending on whether a symbol is (already) exported. +mod base { + use kernel::{ + bindings, + prelude::*, // + }; + + #[inline(never)] + #[allow(clippy::missing_safety_doc)] + pub(super) unsafe fn devres_node_init( + node: *mut bindings::devres_node, + release: bindings::dr_node_release_t, + free: bindings::dr_node_free_t, + ) { + // SAFETY: Safety requirements are the same as `bindings::devres_node_init`. + unsafe { bindings::devres_node_init(node, release, free) } + } + + #[inline(never)] + #[allow(clippy::missing_safety_doc)] + pub(super) unsafe fn devres_set_node_dbginfo( + node: *mut bindings::devres_node, + name: *const c_char, + size: usize, + ) { + // SAFETY: Safety requirements are the same as `bindings::devres_set_node_dbginfo`. + unsafe { bindings::devres_set_node_dbginfo(node, name, size) } + } + + #[inline(never)] + #[allow(clippy::missing_safety_doc)] + pub(super) unsafe fn devres_node_add( + dev: *mut bindings::device, + node: *mut bindings::devres_node, + ) { + // SAFETY: Safety requirements are the same as `bindings::devres_node_add`. + unsafe { bindings::devres_node_add(dev, node) } + } + + #[must_use] + #[inline(never)] + #[allow(clippy::missing_safety_doc)] + pub(super) unsafe fn devres_node_remove( + dev: *mut bindings::device, + node: *mut bindings::devres_node, + ) -> bool { + // SAFETY: Safety requirements are the same as `bindings::devres_node_remove`. + unsafe { bindings::devres_node_remove(dev, node) } + } } impl Devres { @@ -128,58 +193,86 @@ impl Devres { where Error: From, { - let callback = Self::devres_callback; - let data = Arc::pin_init(Revocable::new(data), GFP_KERNEL)?; - let devres_data = data.clone(); + let inner = Arc::pin_init::( + try_pin_init!(Inner { + node <- Opaque::ffi_init(|node: *mut bindings::devres_node| { + // SAFETY: `node` is a valid pointer to an uninitialized `struct devres_node`. + unsafe { + base::devres_node_init( + node, + Some(Self::devres_node_release), + Some(Self::devres_node_free_node), + ) + }; + + // SAFETY: `node` is a valid pointer to an uninitialized `struct devres_node`. + unsafe { + base::devres_set_node_dbginfo( + node, + // TODO: Use `core::any::type_name::()` once it is a `const fn`, + // such that we can convert the `&str` to a `&CStr` at compile-time. + c"Devres".as_char_ptr(), + core::mem::size_of::>(), + ) + }; + }), + data <- Revocable::new(data), + }), + GFP_KERNEL, + )?; // SAFETY: - // - `dev.as_raw()` is a pointer to a valid bound device. - // - `data` is guaranteed to be a valid for the duration of the lifetime of `Self`. - // - `devm_add_action()` is guaranteed not to call `callback` for the entire lifetime of - // `dev`. - to_result(unsafe { - bindings::devm_add_action( - dev.as_raw(), - Some(callback), - Arc::as_ptr(&data).cast_mut().cast(), - ) - })?; - - // `devm_add_action()` was successful and has consumed the reference count. - core::mem::forget(devres_data); + // - `dev` is a valid pointer to a bound `struct device`. + // - `node` is a valid pointer to a `struct devres_node`. + // - `devres_node_add()` is guaranteed not to call `devres_node_release()` for the entire + // lifetime of `dev`. + unsafe { base::devres_node_add(dev.as_raw(), inner.node.get()) }; + + // Take additional reference count for `devres_node_add()`. + core::mem::forget(inner.clone()); Ok(Self { dev: dev.into(), - callback, - data, + inner, }) } fn data(&self) -> &Revocable { - &self.data + &self.inner.data } #[allow(clippy::missing_safety_doc)] - unsafe extern "C" fn devres_callback(ptr: *mut kernel::ffi::c_void) { - // SAFETY: In `Self::new` we've passed a valid pointer of `Revocable` to - // `devm_add_action()`, hence `ptr` must be a valid pointer to `Revocable`. - let data = unsafe { Arc::from_raw(ptr.cast::>()) }; + unsafe extern "C" fn devres_node_release( + _dev: *mut bindings::device, + node: *mut bindings::devres_node, + ) { + let node = Opaque::cast_from(node); + + // SAFETY: `node` is in the same allocation as its container. + let inner = unsafe { kernel::container_of!(node, Inner, node) }; + + // SAFETY: `inner` is a valid `Inner` pointer. + let inner = unsafe { &*inner }; + + inner.data.revoke(); + } + + #[allow(clippy::missing_safety_doc)] + unsafe extern "C" fn devres_node_free_node(node: *mut bindings::devres_node) { + let node = Opaque::cast_from(node); + + // SAFETY: `node` is in the same allocation as its container. + let inner = unsafe { kernel::container_of!(node, Inner, node) }; - data.revoke(); + // SAFETY: `inner` points to the entire `Inner` allocation. + drop(unsafe { Arc::from_raw(inner) }); } - fn remove_action(&self) -> bool { + fn remove_node(&self) -> bool { // SAFETY: - // - `self.dev` is a valid `Device`, - // - the `action` and `data` pointers are the exact same ones as given to - // `devm_add_action()` previously, - (unsafe { - bindings::devm_remove_action_nowarn( - self.dev.as_raw(), - Some(self.callback), - core::ptr::from_ref(self.data()).cast_mut().cast(), - ) - } == 0) + // - `self.device().as_raw()` is a valid pointer to a bound `struct device`. + // - `self.inner.node.get()` is a valid pointer to a `struct devres_node`. + unsafe { base::devres_node_remove(self.device().as_raw(), self.inner.node.get()) } } /// Return a reference of the [`Device`] this [`Devres`] instance has been created with. @@ -261,12 +354,12 @@ impl Drop for Devres { // SAFETY: When `drop` runs, it is guaranteed that nobody is accessing the revocable data // anymore, hence it is safe not to wait for the grace period to finish. if unsafe { self.data().revoke_nosync() } { - // We revoked `self.data` before the devres action did, hence try to remove it. - if self.remove_action() { + // We revoked `self.data` before devres did, hence try to remove it. + if self.remove_node() { // SAFETY: In `Self::new` we have taken an additional reference count of `self.data` - // for `devm_add_action()`. Since `remove_action()` was successful, we have to drop + // for `devres_node_add()`. Since `remove_node()` was successful, we have to drop // this additional reference count. - drop(unsafe { Arc::from_raw(Arc::as_ptr(&self.data)) }); + drop(unsafe { Arc::from_raw(Arc::as_ptr(&self.inner)) }); } } }