[PATCH v5] rust: aref: make `AlwaysRefCounted::inc_ref` an associated function

[PATCH v5] rust: aref: make `AlwaysRefCounted::inc_ref` an associated function

[Trevor Chan]

`AlwaysRefCounted::inc_ref` is a function that shouldn't be called lightly.

To prevent accidentally calling it, change `inc_ref` to be an associated function.

Modify all `AlwaysRefCounted` implementors to work with this change.

Suggested-by: Benno Lossin <lossin@kernel.org>
Link: https://github.com/Rust-for-Linux/linux/issues/1177
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Trevor Chan <trev@trevrosa.dev>
---
Changes in v2:
 - Don't word wrap the patch
Changes in v3:
 - Make argument name of `Empty::inc_ref` consistent with `Empty::dec_ref` 
Changes in v4:
 - Rebase to new rust-next, change new implementors
 - Reword explanation for change in `AlwaysRefCounted::inc_ref` doc comment
Changes in v5:
 - Change commit message to be imperative
---
 rust/kernel/auxiliary.rs        | 4 ++--
 rust/kernel/block/mq/request.rs | 4 ++--
 rust/kernel/cred.rs             | 4 ++--
 rust/kernel/device.rs           | 4 ++--
 rust/kernel/device/property.rs  | 4 ++--
 rust/kernel/drm/device.rs       | 4 ++--
 rust/kernel/drm/gem/mod.rs      | 4 ++--
 rust/kernel/fs/file.rs          | 8 ++++----
 rust/kernel/i2c.rs              | 8 ++++----
 rust/kernel/mm.rs               | 8 ++++----
 rust/kernel/mm/mmput_async.rs   | 4 ++--
 rust/kernel/pci.rs              | 4 ++--
 rust/kernel/pid_namespace.rs    | 4 ++--
 rust/kernel/platform.rs         | 4 ++--
 rust/kernel/sync/aref.rs        | 9 ++++++---
 rust/kernel/task.rs             | 4 ++--
 rust/kernel/usb.rs              | 8 ++++----
 17 files changed, 46 insertions(+), 43 deletions(-)

diff --git a/rust/kernel/auxiliary.rs b/rust/kernel/auxiliary.rs
index c42928d5a239..75a61b51cf79 100644
--- a/rust/kernel/auxiliary.rs
+++ b/rust/kernel/auxiliary.rs
@@ -345,9 +345,9 @@ unsafe impl<Ctx: device::DeviceContext> device::AsBusDevice<Ctx> for Device<Ctx>
 
 // SAFETY: Instances of `Device` are always reference-counted.
 unsafe impl crate::sync::aref::AlwaysRefCounted for Device {
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero.
-        unsafe { bindings::get_device(self.as_ref().as_raw()) };
+        unsafe { bindings::get_device(obj.as_ref().as_raw()) };
     }
 
     unsafe fn dec_ref(obj: NonNull<Self>) {
diff --git a/rust/kernel/block/mq/request.rs b/rust/kernel/block/mq/request.rs
index ce3e30c81cb5..f41d01ea4595 100644
--- a/rust/kernel/block/mq/request.rs
+++ b/rust/kernel/block/mq/request.rs
@@ -234,8 +234,8 @@ unsafe impl<T: Operations> Sync for Request<T> {}
 // keeps the object alive in memory at least until a matching reference count
 // decrement is executed.
 unsafe impl<T: Operations> AlwaysRefCounted for Request<T> {
-    fn inc_ref(&self) {
-        self.wrapper_ref().refcount().inc();
+    fn inc_ref(obj: &Self) {
+        obj.wrapper_ref().refcount().inc();
     }
 
     unsafe fn dec_ref(obj: core::ptr::NonNull<Self>) {
diff --git a/rust/kernel/cred.rs b/rust/kernel/cred.rs
index ffa156b9df37..d53cbc792fa3 100644
--- a/rust/kernel/cred.rs
+++ b/rust/kernel/cred.rs
@@ -78,9 +78,9 @@ pub fn euid(&self) -> Kuid {
 // SAFETY: The type invariants guarantee that `Credential` is always ref-counted.
 unsafe impl AlwaysRefCounted for Credential {
     #[inline]
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The existence of a shared reference means that the refcount is nonzero.
-        unsafe { bindings::get_cred(self.0.get()) };
+        unsafe { bindings::get_cred(obj.0.get()) };
     }
 
     #[inline]
diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
index 645afc49a27d..ec44dcc405d5 100644
--- a/rust/kernel/device.rs
+++ b/rust/kernel/device.rs
@@ -449,9 +449,9 @@ pub fn name(&self) -> &CStr {
 
 // SAFETY: Instances of `Device` are always reference-counted.
 unsafe impl crate::sync::aref::AlwaysRefCounted for Device {
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero.
-        unsafe { bindings::get_device(self.as_raw()) };
+        unsafe { bindings::get_device(obj.as_raw()) };
     }
 
     unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs
index 5aead835fbbc..c39ccc1458b9 100644
--- a/rust/kernel/device/property.rs
+++ b/rust/kernel/device/property.rs
@@ -361,10 +361,10 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 
 // SAFETY: Instances of `FwNode` are always reference-counted.
 unsafe impl crate::sync::aref::AlwaysRefCounted for FwNode {
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The existence of a shared reference guarantees that the
         // refcount is non-zero.
-        unsafe { bindings::fwnode_handle_get(self.as_raw()) };
+        unsafe { bindings::fwnode_handle_get(obj.as_raw()) };
     }
 
     unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs
index 477cf771fb10..0c70ec010bd9 100644
--- a/rust/kernel/drm/device.rs
+++ b/rust/kernel/drm/device.rs
@@ -363,9 +363,9 @@ fn deref(&self) -> &Self::Target {
 // SAFETY: DRM device objects are always reference counted and the get/put functions
 // satisfy the requirements.
 unsafe impl<T: drm::Driver, C: DeviceContext> AlwaysRefCounted for Device<T, C> {
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero.
-        unsafe { bindings::drm_dev_get(self.as_raw()) };
+        unsafe { bindings::drm_dev_get(obj.as_raw()) };
     }
 
     unsafe fn dec_ref(obj: NonNull<Self>) {
diff --git a/rust/kernel/drm/gem/mod.rs b/rust/kernel/drm/gem/mod.rs
index c8b66d816871..ee9e412066ab 100644
--- a/rust/kernel/drm/gem/mod.rs
+++ b/rust/kernel/drm/gem/mod.rs
@@ -52,10 +52,10 @@ unsafe impl $( <$( $tparam_id ),+> )? $crate::sync::aref::AlwaysRefCounted for $
             Self: IntoGEMObject,
             $( $( $bind_param : $bind_trait ),+ )?
         {
-            fn inc_ref(&self) {
+            fn inc_ref(obj: &Self) {
                 // SAFETY: The existence of a shared reference guarantees that the refcount is
                 // non-zero.
-                unsafe { bindings::drm_gem_object_get(self.as_raw()) };
+                unsafe { bindings::drm_gem_object_get(obj.as_raw()) };
             }
 
             unsafe fn dec_ref(obj: core::ptr::NonNull<Self>) {
diff --git a/rust/kernel/fs/file.rs b/rust/kernel/fs/file.rs
index 23ee689bd240..8e5967afcd11 100644
--- a/rust/kernel/fs/file.rs
+++ b/rust/kernel/fs/file.rs
@@ -199,9 +199,9 @@ unsafe impl Sync for File {}
 // makes `ARef<File>` own a normal refcount.
 unsafe impl AlwaysRefCounted for File {
     #[inline]
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The existence of a shared reference means that the refcount is nonzero.
-        unsafe { bindings::get_file(self.as_ptr()) };
+        unsafe { bindings::get_file(obj.as_ptr()) };
     }
 
     #[inline]
@@ -235,9 +235,9 @@ pub struct LocalFile {
 // makes `ARef<LocalFile>` own a normal refcount.
 unsafe impl AlwaysRefCounted for LocalFile {
     #[inline]
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The existence of a shared reference means that the refcount is nonzero.
-        unsafe { bindings::get_file(self.as_ptr()) };
+        unsafe { bindings::get_file(obj.as_ptr()) };
     }
 
     #[inline]
diff --git a/rust/kernel/i2c.rs b/rust/kernel/i2c.rs
index 624b971ca8b0..1a9882a64c4b 100644
--- a/rust/kernel/i2c.rs
+++ b/rust/kernel/i2c.rs
@@ -425,9 +425,9 @@ pub fn get(index: i32) -> Result<ARef<Self>> {
 
 // SAFETY: Instances of `I2cAdapter` are always reference-counted.
 unsafe impl AlwaysRefCounted for I2cAdapter {
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero.
-        unsafe { bindings::i2c_get_adapter(self.index()) };
+        unsafe { bindings::i2c_get_adapter(obj.index()) };
     }
 
     unsafe fn dec_ref(obj: NonNull<Self>) {
@@ -501,9 +501,9 @@ unsafe impl<Ctx: device::DeviceContext> device::AsBusDevice<Ctx> for I2cClient<C
 
 // SAFETY: Instances of `I2cClient` are always reference-counted.
 unsafe impl AlwaysRefCounted for I2cClient {
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero.
-        unsafe { bindings::get_device(self.as_ref().as_raw()) };
+        unsafe { bindings::get_device(obj.as_ref().as_raw()) };
     }
 
     unsafe fn dec_ref(obj: NonNull<Self>) {
diff --git a/rust/kernel/mm.rs b/rust/kernel/mm.rs
index 4764d7b68f2a..c955cbd884b8 100644
--- a/rust/kernel/mm.rs
+++ b/rust/kernel/mm.rs
@@ -57,9 +57,9 @@ unsafe impl Sync for Mm {}
 // SAFETY: By the type invariants, this type is always refcounted.
 unsafe impl AlwaysRefCounted for Mm {
     #[inline]
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The pointer is valid since self is a reference.
-        unsafe { bindings::mmgrab(self.as_raw()) };
+        unsafe { bindings::mmgrab(obj.as_raw()) };
     }
 
     #[inline]
@@ -93,9 +93,9 @@ unsafe impl Sync for MmWithUser {}
 // SAFETY: By the type invariants, this type is always refcounted.
 unsafe impl AlwaysRefCounted for MmWithUser {
     #[inline]
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The pointer is valid since self is a reference.
-        unsafe { bindings::mmget(self.as_raw()) };
+        unsafe { bindings::mmget(obj.as_raw()) };
     }
 
     #[inline]
diff --git a/rust/kernel/mm/mmput_async.rs b/rust/kernel/mm/mmput_async.rs
index b8d2f051225c..7df40777654c 100644
--- a/rust/kernel/mm/mmput_async.rs
+++ b/rust/kernel/mm/mmput_async.rs
@@ -36,9 +36,9 @@ unsafe impl Sync for MmWithUserAsync {}
 // SAFETY: By the type invariants, this type is always refcounted.
 unsafe impl AlwaysRefCounted for MmWithUserAsync {
     #[inline]
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The pointer is valid since self is a reference.
-        unsafe { bindings::mmget(self.as_raw()) };
+        unsafe { bindings::mmget(obj.as_raw()) };
     }
 
     #[inline]
diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
index 5071cae6543f..0f16cf0da3d7 100644
--- a/rust/kernel/pci.rs
+++ b/rust/kernel/pci.rs
@@ -482,9 +482,9 @@ impl<'a> crate::dma::Device<'a> for Device<device::Core<'a>> {}
 
 // SAFETY: Instances of `Device` are always reference-counted.
 unsafe impl crate::sync::aref::AlwaysRefCounted for Device {
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero.
-        unsafe { bindings::pci_dev_get(self.as_raw()) };
+        unsafe { bindings::pci_dev_get(obj.as_raw()) };
     }
 
     unsafe fn dec_ref(obj: NonNull<Self>) {
diff --git a/rust/kernel/pid_namespace.rs b/rust/kernel/pid_namespace.rs
index 979a9718f153..381c9f980b1f 100644
--- a/rust/kernel/pid_namespace.rs
+++ b/rust/kernel/pid_namespace.rs
@@ -43,9 +43,9 @@ pub unsafe fn from_ptr<'a>(ptr: *const bindings::pid_namespace) -> &'a Self {
 // SAFETY: Instances of `PidNamespace` are always reference-counted.
 unsafe impl AlwaysRefCounted for PidNamespace {
     #[inline]
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The existence of a shared reference means that the refcount is nonzero.
-        unsafe { bindings::get_pid_ns(self.as_ptr()) };
+        unsafe { bindings::get_pid_ns(obj.as_ptr()) };
     }
 
     #[inline]
diff --git a/rust/kernel/platform.rs b/rust/kernel/platform.rs
index 9b362e0495d3..85068ae5a405 100644
--- a/rust/kernel/platform.rs
+++ b/rust/kernel/platform.rs
@@ -519,9 +519,9 @@ impl<'a> crate::dma::Device<'a> for Device<device::Core<'a>> {}
 
 // SAFETY: Instances of `Device` are always reference-counted.
 unsafe impl crate::sync::aref::AlwaysRefCounted for Device {
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero.
-        unsafe { bindings::get_device(self.as_ref().as_raw()) };
+        unsafe { bindings::get_device(obj.as_ref().as_raw()) };
     }
 
     unsafe fn dec_ref(obj: NonNull<Self>) {
diff --git a/rust/kernel/sync/aref.rs b/rust/kernel/sync/aref.rs
index b721b2e00b98..2ae2130d5bb1 100644
--- a/rust/kernel/sync/aref.rs
+++ b/rust/kernel/sync/aref.rs
@@ -44,7 +44,10 @@
 /// alive.)
 pub unsafe trait AlwaysRefCounted {
     /// Increments the reference count on the object.
-    fn inc_ref(&self);
+    ///
+    /// This function should not be called accidentally; a type might declare their own `inc_ref`
+    /// function and it shouldn't be confused with this one.
+    fn inc_ref(obj: &Self);
 
     /// Decrements the reference count on the object.
     ///
@@ -145,7 +148,7 @@ pub fn into_raw(me: Self) -> NonNull<T> {
 
 impl<T: AlwaysRefCounted> Clone for ARef<T> {
     fn clone(&self) -> Self {
-        self.inc_ref();
+        T::inc_ref(self);
         // SAFETY: We just incremented the refcount above.
         unsafe { Self::from_raw(self.ptr) }
     }
@@ -162,7 +165,7 @@ fn deref(&self) -> &Self::Target {
 
 impl<T: AlwaysRefCounted> From<&T> for ARef<T> {
     fn from(b: &T) -> Self {
-        b.inc_ref();
+        T::inc_ref(b);
         // SAFETY: We just incremented the refcount above.
         unsafe { Self::from_raw(NonNull::from(b)) }
     }
diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
index 38273f4eedb5..a7711e1558c2 100644
--- a/rust/kernel/task.rs
+++ b/rust/kernel/task.rs
@@ -349,9 +349,9 @@ pub fn group_leader(&self) -> &Task {
 // SAFETY: The type invariants guarantee that `Task` is always refcounted.
 unsafe impl crate::sync::aref::AlwaysRefCounted for Task {
     #[inline]
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The existence of a shared reference means that the refcount is nonzero.
-        unsafe { bindings::get_task_struct(self.as_ptr()) };
+        unsafe { bindings::get_task_struct(obj.as_ptr()) };
     }
 
     #[inline]
diff --git a/rust/kernel/usb.rs b/rust/kernel/usb.rs
index 7aff0c82d0af..c039059c1891 100644
--- a/rust/kernel/usb.rs
+++ b/rust/kernel/usb.rs
@@ -393,11 +393,11 @@ fn as_ref(&self) -> &Device {
 
 // SAFETY: Instances of `Interface` are always reference-counted.
 unsafe impl AlwaysRefCounted for Interface {
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The invariants of `Interface` guarantee that `self.as_raw()`
         // returns a valid `struct usb_interface` pointer, for which we will
         // acquire a new refcount.
-        unsafe { bindings::usb_get_intf(self.as_raw()) };
+        unsafe { bindings::usb_get_intf(obj.as_raw()) };
     }
 
     unsafe fn dec_ref(obj: NonNull<Self>) {
@@ -444,11 +444,11 @@ fn as_raw(&self) -> *mut bindings::usb_device {
 
 // SAFETY: Instances of `Device` are always reference-counted.
 unsafe impl AlwaysRefCounted for Device {
-    fn inc_ref(&self) {
+    fn inc_ref(obj: &Self) {
         // SAFETY: The invariants of `Device` guarantee that `self.as_raw()`
         // returns a valid `struct usb_device` pointer, for which we will
         // acquire a new refcount.
-        unsafe { bindings::usb_get_dev(self.as_raw()) };
+        unsafe { bindings::usb_get_dev(obj.as_raw()) };
     }
 
     unsafe fn dec_ref(obj: NonNull<Self>) {
-- 
2.47.3

Re: [PATCH v5] rust: aref: make `AlwaysRefCounted::inc_ref` an associated function

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] Un-updated AlwaysRefCounted trait implementations cause conditional compilation and rustdoc test errors.
--

commit 5db284043a909f35f9aed5c1467a5f9cf863972d
Author: Trevor Chan <trev@trevrosa.dev>
rust: aref: make `AlwaysRefCounted::inc_ref` an associated function

This commit changes the AlwaysRefCounted::inc_ref function from a method
to an associated function to prevent accidental calls. It updates the
implementors of this trait to reflect this change.

Link: https://github.com/Rust-for-Linux/linux/issues/1177

> diff --git a/rust/kernel/sync/aref.rs b/rust/kernel/sync/aref.rs
> index b721b2e00b986..2ae2130d5bb1d 100644
> --- a/rust/kernel/sync/aref.rs
> +++ b/rust/kernel/sync/aref.rs
> @@ -44,7 +44,10 @@
>  /// alive.)
>  pub unsafe trait AlwaysRefCounted {
>      /// Increments the reference count on the object.
> -    fn inc_ref(&self);
> +    ///
> +    /// This function should not be called accidentally; a type might declare their own `inc_ref`
> +    /// function and it shouldn't be confused with this one.
> +    fn inc_ref(obj: &Self);

[Severity: Low]
Will this change break the build for conditionally compiled modules and
rustdoc tests that still use the old method signature?

When compiling with CONFIG_RUST_DRM_GPUVM, CONFIG_PM_OPP, or
CONFIG_RUST_PWM_ABSTRACTIONS enabled, it appears this will result in
compiler error E0185 because the following implementations were not updated:

rust/kernel/drm/gpuvm/mod.rs:
unsafe impl<T: DriverGpuVm> AlwaysRefCounted for GpuVm<T> {
    fn inc_ref(&self) {

rust/kernel/drm/gpuvm/vm_bo.rs:
unsafe impl<T: DriverGpuVm> AlwaysRefCounted for GpuVmBo<T> {
    fn inc_ref(&self) {

rust/kernel/opp.rs:
unsafe impl AlwaysRefCounted for OPP {
    #[inline]
    fn inc_ref(&self) {

rust/kernel/pwm.rs:
unsafe impl<T: PwmOps> AlwaysRefCounted for Chip<T> {
    #[inline]
    fn inc_ref(&self) {

Additionally, a rustdoc test in rust/kernel/sync/aref.rs for ARef::into_raw
still implements it using the old signature:

    /// unsafe impl AlwaysRefCounted for Empty {
    ///     fn inc_ref(&self) {}

Should these implementations be updated to use fn inc_ref(obj: &Self) to
match the new trait definition?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260628092853.16550-1-trev@trevrosa.dev?part=1