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Message-ID: <20241004155247.2210469-2-gary@garyguo.net>
Date: Fri, 4 Oct 2024 16:52:22 +0100
From: Gary Guo <gary@...yguo.net>
To: Miguel Ojeda <ojeda@...nel.org>,
Alex Gaynor <alex.gaynor@...il.com>,
Boqun Feng <boqun.feng@...il.com>,
Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Benno Lossin <benno.lossin@...ton.me>,
Andreas Hindborg <a.hindborg@...nel.org>,
Alice Ryhl <aliceryhl@...gle.com>,
Trevor Gross <tmgross@...ch.edu>,
Martin Rodriguez Reboredo <yakoyoku@...il.com>
Cc: Will Deacon <will@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Mark Rutland <mark.rutland@....com>,
Dirk Behme <dirk.behme@...bosch.com>,
linux-kernel@...r.kernel.org,
rust-for-linux@...r.kernel.org
Subject: [PATCH 1/3] rust: implement `kernel::sync::Refcount`
This is a wrapping layer of `include/linux/refcount.h`. Currently only
the most basic operations (read/set/inc/dec/dec_and_test) are implemented,
additional methods can be implemented when they are needed.
Currently the kernel refcount has already been used in `Arc`, however it
calls into FFI directly.
Cc: Will Deacon <will@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: Mark Rutland <mark.rutland@....com>
Signed-off-by: Gary Guo <gary@...yguo.net>
---
rust/helpers/refcount.c | 15 ++++++
rust/kernel/sync.rs | 2 +
rust/kernel/sync/refcount.rs | 94 ++++++++++++++++++++++++++++++++++++
3 files changed, 111 insertions(+)
create mode 100644 rust/kernel/sync/refcount.rs
diff --git a/rust/helpers/refcount.c b/rust/helpers/refcount.c
index f47afc148ec3..39649443426b 100644
--- a/rust/helpers/refcount.c
+++ b/rust/helpers/refcount.c
@@ -8,11 +8,26 @@ refcount_t rust_helper_REFCOUNT_INIT(int n)
return (refcount_t)REFCOUNT_INIT(n);
}
+unsigned int rust_helper_refcount_read(refcount_t *r)
+{
+ return refcount_read(r);
+}
+
+void rust_helper_refcount_set(refcount_t *r, int n)
+{
+ refcount_set(r, n);
+}
+
void rust_helper_refcount_inc(refcount_t *r)
{
refcount_inc(r);
}
+void rust_helper_refcount_dec(refcount_t *r)
+{
+ refcount_dec(r);
+}
+
bool rust_helper_refcount_dec_and_test(refcount_t *r)
{
return refcount_dec_and_test(r);
diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
index 0ab20975a3b5..534f098a44eb 100644
--- a/rust/kernel/sync.rs
+++ b/rust/kernel/sync.rs
@@ -11,12 +11,14 @@
mod condvar;
pub mod lock;
mod locked_by;
+mod refcount;
pub use arc::{Arc, ArcBorrow, UniqueArc};
pub use condvar::{new_condvar, CondVar, CondVarTimeoutResult};
pub use lock::mutex::{new_mutex, Mutex};
pub use lock::spinlock::{new_spinlock, SpinLock};
pub use locked_by::LockedBy;
+pub use refcount::Refcount;
/// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
#[repr(transparent)]
diff --git a/rust/kernel/sync/refcount.rs b/rust/kernel/sync/refcount.rs
new file mode 100644
index 000000000000..4a5b815adc05
--- /dev/null
+++ b/rust/kernel/sync/refcount.rs
@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Atomic reference counting.
+//!
+//! C header: [`include/linux/refcount.h`](srctree/include/linux/refcount.h)
+
+use crate::types::Opaque;
+use core::sync::atomic::AtomicI32;
+
+/// Atomic reference counter.
+///
+/// This type is conceptually an atomic integer, but provides a saturation semantics compared to
+/// normal atomic integers. Values in the negative range when viewed as a signed integer are
+/// saturation (bad) values. For details about the saturation semantics, please refer to top of
+/// [`include/linux/refcount.h`](srctree/include/refcount.h).
+///
+/// Wraps the kernel's C `refcount_t`.
+#[repr(transparent)]
+pub struct Refcount(Opaque<bindings::refcount_t>);
+
+impl Refcount {
+ /// Construct a new [`Refcount`] from an initial value.
+ #[inline]
+ pub fn new(value: i32) -> Self {
+ // SAFETY: There are no safety requirements for this FFI call.
+ Self(Opaque::new(unsafe { bindings::REFCOUNT_INIT(value) }))
+ }
+
+ #[inline]
+ fn as_ptr(&self) -> *mut bindings::refcount_t {
+ self.0.get()
+ }
+
+ /// Get a refcount's value.
+ #[inline]
+ pub fn read(&self) -> i32 {
+ // SAFETY: `self.as_ptr()` is valid.
+ unsafe { bindings::refcount_read(self.as_ptr()) as _ }
+ }
+
+ /// Set a refcount's value.
+ #[inline]
+ pub fn set(&self, value: i32) {
+ // SAFETY: `self.as_ptr()` is valid.
+ unsafe { bindings::refcount_set(self.as_ptr(), value) }
+ }
+
+ /// Increment a refcount.
+ ///
+ /// It will saturate if overflows and `WARN`. It will also `WARN` is the refcount is 0, as this
+ /// represents a possible use-after-free condition.
+ ///
+ /// Provides no memory ordering, it is assumed that caller already has a reference on the
+ /// object.
+ #[inline]
+ pub fn inc(&self) {
+ // SAFETY: self is valid.
+ unsafe { bindings::refcount_inc(self.as_ptr()) }
+ }
+
+ /// Decrement a refcount.
+ ///
+ /// It will `WARN` on underflow and fail to decrement when saturated.
+ ///
+ /// Provides release memory ordering, such that prior loads and stores are done
+ /// before.
+ #[inline]
+ pub fn dec(&self) {
+ // SAFETY: `self.as_ptr()` is valid.
+ unsafe { bindings::refcount_dec(self.as_ptr()) }
+ }
+
+ /// Decrement a refcount and test if it is 0.
+ ///
+ /// It will `WARN` on underflow and fail to decrement when saturated.
+ ///
+ /// Provides release memory ordering, such that prior loads and stores are done
+ /// before, and provides an acquire ordering on success such that memory deallocation
+ /// must come after.
+ ///
+ /// Returns true if the resulting refcount is 0, false otherwise.
+ #[inline]
+ #[must_use = "use `dec` instead you do not need to test if it is 0"]
+ pub fn dec_and_test(&self) -> bool {
+ // SAFETY: `self.as_ptr()` is valid.
+ unsafe { bindings::refcount_dec_and_test(self.as_ptr()) }
+ }
+}
+
+// SAFETY: `refcount_t` is thread-safe.
+unsafe impl Send for Refcount {}
+
+// SAFETY: `refcount_t` is thread-safe.
+unsafe impl Sync for Refcount {}
--
2.44.1
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