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Message-Id: <A12E32E0-9460-48D3-83FE-23C5915179A5@collabora.com>
Date: Thu, 18 Dec 2025 13:00:11 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Boqun Feng <boqun.feng@...il.com>,
Peter Zijlstra <peterz@...radead.org>,
Will Deacon <will@...nel.org>,
Ingo Molnar <mingo@...hat.com>,
Waiman Long <longman@...hat.com>,
Miguel Ojeda <ojeda@...nel.org>,
Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Benno Lossin <lossin@...nel.org>,
Andreas Hindborg <a.hindborg@...nel.org>,
Trevor Gross <tmgross@...ch.edu>,
Danilo Krummrich <dakr@...nel.org>,
linux-kernel@...r.kernel.org,
rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v2] rust: sync: inline various lock related methods
> On 18 Dec 2025, at 09:10, Alice Ryhl <aliceryhl@...gle.com> wrote:
>
> While debugging a different issue [1], I inspected a rust_binder.ko file
> and noticed the following relocation:
>
> R_AARCH64_CALL26 _RNvXNtNtNtCsdfZWD8DztAw_6kernel4sync4lock8spinlockNtB2_15SpinLockBackendNtB4_7Backend6unlock
>
> This relocation (and a similar one for lock) occurred many times
> throughout the module. That is not really useful because all this
> function does is call spin_unlock(), so what we actually want here is
> that a call to spin_unlock() dirctly is generated in favor of this
> wrapper method.
>
> Thus, mark these methods inline.
>
> Link: https://lore.kernel.org/p/20251111-binder-fix-list-remove-v1-0-8ed14a0da63d@google.com
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
> Changes in v2:
> - Rebased on v6.19-rc1.
> - Link to v1: https://lore.kernel.org/r/20251113-inline-lock-unlock-v1-1-1b6e8c323bcf@google.com
> ---
> rust/kernel/sync/lock.rs | 7 +++++++
> rust/kernel/sync/lock/global.rs | 2 ++
> rust/kernel/sync/lock/mutex.rs | 5 +++++
> rust/kernel/sync/lock/spinlock.rs | 5 +++++
> 4 files changed, 19 insertions(+)
>
> diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
> index 46a57d1fc309d330a4c82fe1ecce18297205faed..10b6b5e9b024f2d3ee7458fc2f64190bd38f4391 100644
> --- a/rust/kernel/sync/lock.rs
> +++ b/rust/kernel/sync/lock.rs
> @@ -156,6 +156,7 @@ impl<B: Backend> Lock<(), B> {
> /// the whole lifetime of `'a`.
> ///
> /// [`State`]: Backend::State
> + #[inline]
> pub unsafe fn from_raw<'a>(ptr: *mut B::State) -> &'a Self {
> // SAFETY:
> // - By the safety contract `ptr` must point to a valid initialised instance of `B::State`
> @@ -169,6 +170,7 @@ pub unsafe fn from_raw<'a>(ptr: *mut B::State) -> &'a Self {
>
> impl<T: ?Sized, B: Backend> Lock<T, B> {
> /// Acquires the lock and gives the caller access to the data protected by it.
> + #[inline]
> pub fn lock(&self) -> Guard<'_, T, B> {
> // SAFETY: The constructor of the type calls `init`, so the existence of the object proves
> // that `init` was called.
> @@ -182,6 +184,7 @@ pub fn lock(&self) -> Guard<'_, T, B> {
> /// Returns a guard that can be used to access the data protected by the lock if successful.
> // `Option<T>` is not `#[must_use]` even if `T` is, thus the attribute is needed here.
> #[must_use = "if unused, the lock will be immediately unlocked"]
> + #[inline]
> pub fn try_lock(&self) -> Option<Guard<'_, T, B>> {
> // SAFETY: The constructor of the type calls `init`, so the existence of the object proves
> // that `init` was called.
> @@ -275,6 +278,7 @@ pub fn as_mut(&mut self) -> Pin<&mut T> {
> impl<T: ?Sized, B: Backend> core::ops::Deref for Guard<'_, T, B> {
> type Target = T;
>
> + #[inline]
> fn deref(&self) -> &Self::Target {
> // SAFETY: The caller owns the lock, so it is safe to deref the protected data.
> unsafe { &*self.lock.data.get() }
> @@ -285,6 +289,7 @@ impl<T: ?Sized, B: Backend> core::ops::DerefMut for Guard<'_, T, B>
> where
> T: Unpin,
> {
> + #[inline]
> fn deref_mut(&mut self) -> &mut Self::Target {
> // SAFETY: The caller owns the lock, so it is safe to deref the protected data.
> unsafe { &mut *self.lock.data.get() }
> @@ -292,6 +297,7 @@ fn deref_mut(&mut self) -> &mut Self::Target {
> }
>
> impl<T: ?Sized, B: Backend> Drop for Guard<'_, T, B> {
> + #[inline]
> fn drop(&mut self) {
> // SAFETY: The caller owns the lock, so it is safe to unlock it.
> unsafe { B::unlock(self.lock.state.get(), &self.state) };
> @@ -304,6 +310,7 @@ impl<'a, T: ?Sized, B: Backend> Guard<'a, T, B> {
> /// # Safety
> ///
> /// The caller must ensure that it owns the lock.
> + #[inline]
> pub unsafe fn new(lock: &'a Lock<T, B>, state: B::GuardState) -> Self {
> // SAFETY: The caller can only hold the lock if `Backend::init` has already been called.
> unsafe { B::assert_is_held(lock.state.get()) };
> diff --git a/rust/kernel/sync/lock/global.rs b/rust/kernel/sync/lock/global.rs
> index eab48108a4aebeb72b2026d6c21d5748b0e62f0a..aecbdc34738fbd746de79eb0f1abe995478ad785 100644
> --- a/rust/kernel/sync/lock/global.rs
> +++ b/rust/kernel/sync/lock/global.rs
> @@ -77,6 +77,7 @@ pub unsafe fn init(&'static self) {
> }
>
> /// Lock this global lock.
> + #[inline]
> pub fn lock(&'static self) -> GlobalGuard<B> {
> GlobalGuard {
> inner: self.inner.lock(),
> @@ -84,6 +85,7 @@ pub fn lock(&'static self) -> GlobalGuard<B> {
> }
>
> /// Try to lock this global lock.
> + #[inline]
> pub fn try_lock(&'static self) -> Option<GlobalGuard<B>> {
> Some(GlobalGuard {
> inner: self.inner.try_lock()?,
> diff --git a/rust/kernel/sync/lock/mutex.rs b/rust/kernel/sync/lock/mutex.rs
> index 581cee7ab842ad62ec144e67138676c000a3f5e4..cda0203efefb9fcb32c7eab28721e8678ccec575 100644
> --- a/rust/kernel/sync/lock/mutex.rs
> +++ b/rust/kernel/sync/lock/mutex.rs
> @@ -102,6 +102,7 @@ unsafe impl super::Backend for MutexBackend {
> type State = bindings::mutex;
> type GuardState = ();
>
> + #[inline]
> unsafe fn init(
> ptr: *mut Self::State,
> name: *const crate::ffi::c_char,
> @@ -112,18 +113,21 @@ unsafe fn init(
> unsafe { bindings::__mutex_init(ptr, name, key) }
> }
>
> + #[inline]
> unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState {
> // SAFETY: The safety requirements of this function ensure that `ptr` points to valid
> // memory, and that it has been initialised before.
> unsafe { bindings::mutex_lock(ptr) };
> }
>
> + #[inline]
> unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) {
> // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the
> // caller is the owner of the mutex.
> unsafe { bindings::mutex_unlock(ptr) };
> }
>
> + #[inline]
> unsafe fn try_lock(ptr: *mut Self::State) -> Option<Self::GuardState> {
> // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
> let result = unsafe { bindings::mutex_trylock(ptr) };
> @@ -135,6 +139,7 @@ unsafe fn try_lock(ptr: *mut Self::State) -> Option<Self::GuardState> {
> }
> }
>
> + #[inline]
> unsafe fn assert_is_held(ptr: *mut Self::State) {
> // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
> unsafe { bindings::mutex_assert_is_held(ptr) }
> diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
> index d7be38ccbdc7dc4d70caaed0e7088f59f65fc6d1..ef76fa07ca3a2b5e32e956e828be5b295da0bc28 100644
> --- a/rust/kernel/sync/lock/spinlock.rs
> +++ b/rust/kernel/sync/lock/spinlock.rs
> @@ -101,6 +101,7 @@ unsafe impl super::Backend for SpinLockBackend {
> type State = bindings::spinlock_t;
> type GuardState = ();
>
> + #[inline]
> unsafe fn init(
> ptr: *mut Self::State,
> name: *const crate::ffi::c_char,
> @@ -111,18 +112,21 @@ unsafe fn init(
> unsafe { bindings::__spin_lock_init(ptr, name, key) }
> }
>
> + #[inline]
> unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState {
> // SAFETY: The safety requirements of this function ensure that `ptr` points to valid
> // memory, and that it has been initialised before.
> unsafe { bindings::spin_lock(ptr) }
> }
>
> + #[inline]
> unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) {
> // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the
> // caller is the owner of the spinlock.
> unsafe { bindings::spin_unlock(ptr) }
> }
>
> + #[inline]
> unsafe fn try_lock(ptr: *mut Self::State) -> Option<Self::GuardState> {
> // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
> let result = unsafe { bindings::spin_trylock(ptr) };
> @@ -134,6 +138,7 @@ unsafe fn try_lock(ptr: *mut Self::State) -> Option<Self::GuardState> {
> }
> }
>
> + #[inline]
> unsafe fn assert_is_held(ptr: *mut Self::State) {
> // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
> unsafe { bindings::spin_assert_is_held(ptr) }
>
> ---
> base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
> change-id: 20251113-inline-lock-unlock-b1726632a99d
>
> Best regards,
> --
> Alice Ryhl <aliceryhl@...gle.com>
>
>
I wonder if _everything_ has to be inlined, i.e.: even things like assert_is_held(), init() and etc.
In any case,
Reviewed-by: Daniel Almeida <daniel.almeida@...labora.com>
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