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Message-ID: <20241018232306.476664-2-lyude@redhat.com>
Date: Fri, 18 Oct 2024 19:22:25 -0400
From: Lyude Paul <lyude@...hat.com>
To: rust-for-linux@...r.kernel.org
Cc: Danilo Krummrich <dakr@...hat.com>,
airlied@...hat.com,
Ingo Molnar <mingo@...hat.com>,
Will Deacon <will@...nel.org>,
Waiman Long <longman@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
linux-kernel@...r.kernel.org,
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>,
Wedson Almeida Filho <wedsonaf@...il.com>,
Danilo Krummrich <dakr@...nel.org>,
FUJITA Tomonori <fujita.tomonori@...il.com>,
Valentin Obst <kernel@...entinobst.de>
Subject: [PATCH v8 1/3] rust: Introduce local_irq module
This introduces a module for adding marker types to indicate the type of
interrupt context a function is called in. Note that nothing here enables
or disables interrupts on its own, this is simply for verifying correctness
at compile-time.
Signed-off-by: Lyude Paul <lyude@...hat.com>
---
V2:
* Actually make it so that we check whether or not we have interrupts
disabled with debug assertions
* Fix issues in the documentation (added suggestions, missing periods, made
sure that all rustdoc examples compile properly)
* Pass IrqDisabled by value, not reference
* Ensure that IrqDisabled is !Send and !Sync using
PhantomData<(&'a (), *mut ())>
* Add all of the suggested derives from Benno Lossin
V3:
* Use `impl` for FnOnce bounds in with_irqs_disabled()
* Use higher-ranked trait bounds for the lifetime of with_irqs_disabled()
* Wording changes in the documentation for the module itself
V4:
* Use the actual unsafe constructor for IrqDisabled in
with_irqs_disabled()
* Fix comment style in with_irqs_disabled example
* Check before calling local_irq_restore() in with_irqs_disabled that
interrupts are still disabled. It would have been nice to do this from a
Drop implementation like I hoped, but I realized rust doesn't allow that
for types that implement Copy.
* Document that interrupts can't be re-enabled within the `cb` provided to
`with_irqs_disabled`, and link to the github issue I just filed about
this that describes the solution for this.
V5:
* Rebase against rust-next for the helpers split
* Fix typo (enabled -> disabled) - Dirk
V6:
* s/indicate/require/ in IrqDisabled docs
* Reword comment above with_irqs_disabled in code example requested by
Benno
* Add paragraph to with_irqs_disabled docs requested by Benno
* Apply the comments from Boqun's review for V4 that I missed
* Document type invariants of `IrqDisabled`
V7:
* Change name of module to local_irq.rs
* Remove with_interrupts_disabled()
* Update documentation wording a bit to make mention of PREEMPT_RT
This patch depends on
https://lore.kernel.org/rust-for-linux/20240808-alice-file-v9-1-2cb7b934e0e1@google.com/
Signed-off-by: Lyude Paul <lyude@...hat.com>
---
rust/helpers/helpers.c | 1 +
rust/helpers/irq.c | 8 ++++++
rust/kernel/lib.rs | 1 +
rust/kernel/local_irq.rs | 56 ++++++++++++++++++++++++++++++++++++++++
4 files changed, 66 insertions(+)
create mode 100644 rust/helpers/irq.c
create mode 100644 rust/kernel/local_irq.rs
diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 20a0c69d5cc7b..fd70afe5069ca 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -12,6 +12,7 @@
#include "build_assert.c"
#include "build_bug.c"
#include "err.c"
+#include "irq.c"
#include "kunit.c"
#include "mutex.c"
#include "page.c"
diff --git a/rust/helpers/irq.c b/rust/helpers/irq.c
new file mode 100644
index 0000000000000..d129094cc1940
--- /dev/null
+++ b/rust/helpers/irq.c
@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/irqflags.h>
+
+bool rust_helper_irqs_disabled(void)
+{
+ return irqs_disabled();
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 620de74d128f9..b7e604bc968ce 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -40,6 +40,7 @@
#[cfg(CONFIG_KUNIT)]
pub mod kunit;
pub mod list;
+pub mod local_irq;
#[cfg(CONFIG_NET)]
pub mod net;
pub mod page;
diff --git a/rust/kernel/local_irq.rs b/rust/kernel/local_irq.rs
new file mode 100644
index 0000000000000..e9e82347392c7
--- /dev/null
+++ b/rust/kernel/local_irq.rs
@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Interrupt controls
+//!
+//! This module allows Rust code to annotate functions which can only be called in contexts where
+//! local interrupts on the CPU may be disabled.
+
+use crate::types::NotThreadSafe;
+use bindings;
+use core::marker::*;
+
+/// A token that is only available in contexts where interrupts are disabled on non-PREEMPT_RT
+/// kernels.
+///
+/// [`IrqDisabled`] is marker made available when local processor interrupts are disabled on
+/// non-PREEMPT_RT kernels. A function may require a [`IrqDisabled`] to ensure that functions may
+/// only be run with processor interrupts disabled on such kernels.
+///
+/// This is a marker type; it has no size, and is simply used as a compile-time guarantee that
+/// interrupts are disabled where required.
+///
+/// # Invariants
+///
+/// On kernels where `CONFIG_PREEMPT_RT=n` is set in the kernel config, local processor interrupts
+/// are disabled whenever an object of this type exists.
+#[derive(Copy, Clone, Debug, Ord, Eq, PartialOrd, PartialEq, Hash)]
+pub struct IrqDisabled<'a>(PhantomData<(&'a (), NotThreadSafe)>);
+
+impl IrqDisabled<'_> {
+ /// Create a new [`IrqDisabled`] token in an interrupt disabled context.
+ ///
+ /// This creates a [`IrqDisabled`] token, which can be passed to functions that must
+ /// be run without interrupts on kernels where `CONFIG_PREEMPT_RT=n`. If debug assertions are
+ /// enabled, this function will assert that interrupts match the expected state. Otherwise, it
+ /// has no size or cost at runtime.
+ ///
+ /// # Panics
+ ///
+ /// If debug assertions are enabled, then this function will assert on non-PREEMPT_RT kernels
+ /// that local processor interrupts are disabled upon creation.
+ ///
+ /// # Safety
+ ///
+ /// This function must only be called in contexts where it is known that on a non-PREEMPT_RT
+ /// kernel, local interrupts have been disabled for the current CPU. The user is making a
+ /// promise that they will remain disabled at least until this [`IrqDisabled`] is
+ /// dropped.
+ pub unsafe fn new() -> Self {
+ // SAFETY: FFI call with no special requirements
+ debug_assert!(unsafe { bindings::irqs_disabled() });
+
+ // INVARIANT: The safety requirements of this function ensure that IRQs are disabled on
+ // non-PREEMPT_RT kernels.
+ Self(PhantomData)
+ }
+}
--
2.47.0
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