Re: [PATCH RFC 1/2] rust: sync: introduce a way to create lock class from caller

[lyude@redhat.com]

Reviewed-by: Lyude Paul <lyude@redhat.com>

On Fri, 2026-07-03 at 14:47 +0100, Gary Guo wrote:
> Rust provides a `#[track_caller]` mechanism that can be used to
> identify
> callers from callees. This also works across multiple level of calls.
> As lockdep only needs the address for static key classes, the address
> of
> these `&'static Location` can be used as unique lock class keys.
> This allows a more implicit way of creating lock classes without
> having to
> use macros.
> 
> Create `LockClassKey::from_caller`, and use it for mutex and
> spinlocks.
> 
> Signed-off-by: Gary Guo <gary@garyguo.net>
> ---
>  rust/kernel/sync.rs               | 37
> +++++++++++++++++++++++++++++++++----
>  rust/kernel/sync/lock.rs          | 13 +++++++++++--
>  rust/kernel/sync/lock/mutex.rs    |  3 +--
>  rust/kernel/sync/lock/spinlock.rs |  3 +--
>  4 files changed, 46 insertions(+), 10 deletions(-)
> 
> diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
> index 993dbf2caa0e..cf76fb37c460 100644
> --- a/rust/kernel/sync.rs
> +++ b/rust/kernel/sync.rs
> @@ -5,8 +5,12 @@
>  //! This module contains the kernel APIs related to synchronisation
> that have been ported or
>  //! wrapped for usage by Rust code in the kernel.
>  
> -use crate::prelude::*;
> -use crate::types::Opaque;
> +use core::panic::Location;
> +
> +use crate::{
> +    prelude::*,
> +    types::Opaque, //
> +};
>  use pin_init;
>  
>  mod arc;
> @@ -66,6 +70,31 @@ impl LockClassKey {
>          }
>      }
>  
> +    /// Obtain a statically allocated lock class key identified by
> the caller's location.
> +    ///
> +    /// Different caller locations will be guaranteed to have
> different lock class keys; however for
> +    /// the same caller location, this may return different keys,
> e.g. if the caller is instantiated
> +    /// in different object files.
> +    #[inline]
> +    #[track_caller]
> +    pub const fn from_caller() -> Pin<&'static Self> {
> +        static_assert!(size_of::<Location<'_>>() >=
> size_of::<LockClassKey>());
> +
> +        #[cfg(CONFIG_LOCKDEP)]
> +        {
> +            let caller = Location::caller();
> +            // SAFETY: For static objects, lockdep does not touch
> the underlying memory, and only
> +            // the address matters. `Location::caller()` is in
> rodata so it meets the requirement.
> +            // The size check above makes sure that it does not
> overlap with other lock class keys.
> +            unsafe {
> Pin::new_unchecked(&*core::ptr::from_ref(caller).cast::<Self>()) }
> +        }
> +
> +        // A separate version if lockdep is disabled to avoid
> unnecessary `Location` being
> +        // generated.
> +        #[cfg(not(CONFIG_LOCKDEP))]
> +        static_lock_class!()
> +    }
> +
>      /// Initializes a dynamically allocated lock class key.
>      ///
>      /// In the common case of using a statically allocated lock
> class key, the
> @@ -83,7 +112,7 @@ impl LockClassKey {
>      /// let key_ptr = key.into_foreign();
>      ///
>      /// {
> -    ///     stack_pin_init!(let num: SpinLock<u32> = SpinLock::new(
> +    ///     stack_pin_init!(let num: SpinLock<u32> =
> SpinLock::new_with_lock_class(
>      ///         0,
>      ///         c"my_spinlock",
>      ///         // SAFETY: `key_ptr` is returned by the above
> `into_foreign()`, whose
> @@ -129,7 +158,7 @@ fn drop(self: Pin<&mut Self>) {
>  /// use kernel::sync::{static_lock_class, Arc, SpinLock};
>  ///
>  /// fn new_locked_int() -> Result<Arc<SpinLock<u32>>> {
> -///     Arc::pin_init(SpinLock::new(
> +///     Arc::pin_init(SpinLock::new_with_lock_class(
>  ///         42,
>  ///         c"new_locked_int",
>  ///         static_lock_class!(),
> diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
> index 10b6b5e9b024..447fec291cdf 100644
> --- a/rust/kernel/sync/lock.rs
> +++ b/rust/kernel/sync/lock.rs
> @@ -127,8 +127,17 @@ unsafe impl<T: ?Sized + Send, B: Backend> Send
> for Lock<T, B> {}
>  unsafe impl<T: ?Sized + Send, B: Backend> Sync for Lock<T, B> {}
>  
>  impl<T, B: Backend> Lock<T, B> {
> -    /// Constructs a new lock initialiser.
> -    pub fn new(
> +    /// Constructs a new lock initialiser with a custom name.
> +    #[inline]
> +    #[track_caller]
> +    pub fn new_with_name(t: impl PinInit<T>, name: &'static CStr) ->
> impl PinInit<Self> {
> +        let key = LockClassKey::from_caller();
> +        Self::new_with_lock_class(t, name, key)
> +    }
> +
> +    /// Constructs a new lock initialiser with a custom name and
> lock class key.
> +    #[inline]
> +    pub fn new_with_lock_class(
>          t: impl PinInit<T>,
>          name: &'static CStr,
>          key: Pin<&'static LockClassKey>,
> diff --git a/rust/kernel/sync/lock/mutex.rs
> b/rust/kernel/sync/lock/mutex.rs
> index cda0203efefb..3675ce244e08 100644
> --- a/rust/kernel/sync/lock/mutex.rs
> +++ b/rust/kernel/sync/lock/mutex.rs
> @@ -11,8 +11,7 @@
>  #[macro_export]
>  macro_rules! new_mutex {
>      ($inner:expr $(, $name:literal)? $(,)?) => {
> -        $crate::sync::Mutex::new(
> -            $inner, $crate::optional_name!($($name)?),
> $crate::static_lock_class!())
> +        $crate::sync::Mutex::new_with_name($inner,
> $crate::optional_name!($($name)?))
>      };
>  }
>  pub use new_mutex;
> diff --git a/rust/kernel/sync/lock/spinlock.rs
> b/rust/kernel/sync/lock/spinlock.rs
> index ef76fa07ca3a..091167ceda66 100644
> --- a/rust/kernel/sync/lock/spinlock.rs
> +++ b/rust/kernel/sync/lock/spinlock.rs
> @@ -11,8 +11,7 @@
>  #[macro_export]
>  macro_rules! new_spinlock {
>      ($inner:expr $(, $name:literal)? $(,)?) => {
> -        $crate::sync::SpinLock::new(
> -            $inner, $crate::optional_name!($($name)?),
> $crate::static_lock_class!())
> +        $crate::sync::SpinLock::new_with_name($inner,
> $crate::optional_name!($($name)?))
>      };
>  }
>  pub use new_spinlock;