linux-kernel - [RFC PATCH 07/11] rust: lock: add support for `Lock::lock

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Message-Id: <20230503090708.2524310-8-nmi@metaspace.dk>
Date:   Wed,  3 May 2023 11:07:04 +0200
From:   Andreas Hindborg <nmi@...aspace.dk>
To:     Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
        Keith Busch <kbusch@...nel.org>,
        Damien Le Moal <Damien.LeMoal@....com>,
        Hannes Reinecke <hare@...e.de>,
        lsf-pc@...ts.linux-foundation.org, rust-for-linux@...r.kernel.org,
        linux-block@...r.kernel.org
Cc:     Wedson Almeida Filho <walmeida@...rosoft.com>,
        Matthew Wilcox <willy@...radead.org>,
        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>,
        Andreas Hindborg <a.hindborg@...sung.com>,
        Andreas Hindborg <nmi@...aspace.dk>,
        linux-kernel@...r.kernel.org (open list), gost.dev@...sung.com
Subject: [RFC PATCH 07/11] rust: lock: add support for `Lock::lock_irqsave`

From: Wedson Almeida Filho <walmeida@...rosoft.com>

This allows locks like spinlocks and raw spinlocks to expose a
`lock_irqsave` variant in Rust that corresponds to the C version.

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@...il.com>
Signed-off-by: Wedson Almeida Filho <walmeida@...rosoft.com>
---
 rust/kernel/sync/lock.rs | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index 1c584b1df30d..bb21af8a8377 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -72,6 +72,44 @@ pub unsafe trait Backend {
     }
 }
 
+/// The "backend" of a lock that supports the irq-save variant.
+///
+/// # Safety
+///
+/// The same requirements wrt mutual exclusion in [`Backend`] apply for acquiring the lock via
+/// [`IrqSaveBackend::lock_irqsave`].
+///
+/// Additionally, when [`IrqSaveBackend::lock_irqsave`] is used to acquire the lock, implementers
+/// must disable interrupts on lock, and restore interrupt state on unlock. Implementers may use
+/// [`Backend::GuardState`] to store state needed to keep track of the interrupt state.
+pub unsafe trait IrqSaveBackend: Backend {
+    /// Acquires the lock, making the caller its owner.
+    ///
+    /// Before acquiring the lock, it disables interrupts, and returns the previous interrupt state
+    /// as its guard state so that the guard can restore it when it is dropped.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure that [`Backend::init`] has been previously called.
+    #[must_use]
+    unsafe fn lock_irqsave(ptr: *mut Self::State) -> Self::GuardState;
+}
+
+impl<T: ?Sized, B: IrqSaveBackend> Lock<T, B> {
+    /// Acquires the lock and gives the caller access to the data protected by it.
+    ///
+    /// Before acquiring the lock, it disables interrupts. When the guard is dropped, the interrupt
+    /// state (either enabled or disabled) is restored to its state before
+    /// [`lock_irqsave`](Self::lock_irqsave) was called.
+    pub fn lock_irqsave(&self) -> Guard<'_, T, B> {
+        // SAFETY: The constructor of the type calls `init`, so the existence of the object proves
+        // that `init` was called.
+        let state = unsafe { B::lock_irqsave(self.state.get()) };
+        // SAFETY: The lock was just acquired.
+        unsafe { Guard::new(self, state) }
+    }
+}
+
 /// A mutual exclusion primitive.
 ///
 /// Exposes one of the kernel locking primitives. Which one is exposed depends on the lock backend
-- 
2.40.0