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Message-Id: <20230714-classless_lockdep-v1-5-229b9671ce31@asahilina.net>
Date: Fri, 14 Jul 2023 18:13:57 +0900
From: Asahi Lina <lina@...hilina.net>
To: Miguel Ojeda <ojeda@...nel.org>,
Alex Gaynor <alex.gaynor@...il.com>,
Wedson Almeida Filho <wedsonaf@...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>,
Masahiro Yamada <masahiroy@...nel.org>,
Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Nicolas Schier <nicolas@...sle.eu>, Tom Rix <trix@...hat.com>,
Daniel Vetter <daniel@...ll.ch>
Cc: Hector Martin <marcan@...can.st>, Sven Peter <sven@...npeter.dev>,
Alyssa Rosenzweig <alyssa@...enzweig.io>,
asahi@...ts.linux.dev, rust-for-linux@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
llvm@...ts.linux.dev, Asahi Lina <lina@...hilina.net>
Subject: [PATCH RFC 05/11] rust: sync: Add dummy LockClassKey
implementation for !CONFIG_LOCKDEP
Lock classes aren't used without lockdep. The C side declares the key
as an empty struct in that case, but let's make it an explicit ZST in
Rust, implemented in a separate module. This allows us to more easily
guarantee that the lockdep code will be trivially optimized out without
CONFIG_LOCKDEP, including LockClassKey arguments that are passed around.
Depending on whether CONFIG_LOCKDEP is enabled or not, we then import
the real lockdep implementation or the dummy one.
Signed-off-by: Asahi Lina <lina@...hilina.net>
---
rust/kernel/sync.rs | 29 ++++++++---------------------
rust/kernel/sync/lockdep.rs | 27 +++++++++++++++++++++++++++
rust/kernel/sync/no_lockdep.rs | 19 +++++++++++++++++++
3 files changed, 54 insertions(+), 21 deletions(-)
diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
index d219ee518eff..352472c6b77a 100644
--- a/rust/kernel/sync.rs
+++ b/rust/kernel/sync.rs
@@ -5,37 +5,24 @@
//! 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::types::Opaque;
-
mod arc;
mod condvar;
pub mod lock;
mod locked_by;
+#[cfg(CONFIG_LOCKDEP)]
+mod lockdep;
+#[cfg(not(CONFIG_LOCKDEP))]
+mod no_lockdep;
+#[cfg(not(CONFIG_LOCKDEP))]
+use no_lockdep as lockdep;
+
pub use arc::{Arc, ArcBorrow, UniqueArc};
pub use condvar::CondVar;
pub use lock::{mutex::Mutex, spinlock::SpinLock};
+pub use lockdep::LockClassKey;
pub use locked_by::LockedBy;
-/// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
-#[repr(transparent)]
-pub struct LockClassKey(Opaque<bindings::lock_class_key>);
-
-// SAFETY: `bindings::lock_class_key` is designed to be used concurrently from multiple threads and
-// provides its own synchronization.
-unsafe impl Sync for LockClassKey {}
-
-impl LockClassKey {
- /// Creates a new lock class key.
- pub const fn new() -> Self {
- Self(Opaque::uninit())
- }
-
- pub(crate) fn as_ptr(&self) -> *mut bindings::lock_class_key {
- self.0.get()
- }
-}
-
/// Defines a new static lock class and returns a pointer to it.
#[doc(hidden)]
#[macro_export]
diff --git a/rust/kernel/sync/lockdep.rs b/rust/kernel/sync/lockdep.rs
new file mode 100644
index 000000000000..cb68b18dc0ad
--- /dev/null
+++ b/rust/kernel/sync/lockdep.rs
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Lockdep utilities.
+//!
+//! This module abstracts the parts of the kernel lockdep API relevant to Rust
+//! modules, including lock classes.
+
+use crate::types::Opaque;
+
+/// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
+#[repr(transparent)]
+pub struct LockClassKey(Opaque<bindings::lock_class_key>);
+
+impl LockClassKey {
+ /// Creates a new lock class key.
+ pub const fn new() -> Self {
+ Self(Opaque::uninit())
+ }
+
+ pub(crate) fn as_ptr(&self) -> *mut bindings::lock_class_key {
+ self.0.get()
+ }
+}
+
+// SAFETY: `bindings::lock_class_key` is designed to be used concurrently from multiple threads and
+// provides its own synchronization.
+unsafe impl Sync for LockClassKey {}
diff --git a/rust/kernel/sync/no_lockdep.rs b/rust/kernel/sync/no_lockdep.rs
new file mode 100644
index 000000000000..69d42e8d9801
--- /dev/null
+++ b/rust/kernel/sync/no_lockdep.rs
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Dummy lockdep utilities.
+//!
+//! Takes the place of the `lockdep` module when lockdep is disabled.
+
+/// A dummy, zero-sized lock class.
+pub struct LockClassKey();
+
+impl LockClassKey {
+ /// Creates a new dummy lock class key.
+ pub const fn new() -> Self {
+ Self()
+ }
+
+ pub(crate) fn as_ptr(&self) -> *mut bindings::lock_class_key {
+ core::ptr::null_mut()
+ }
+}
--
2.40.1
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