Merge pull request #734 from wedsonaf/raw-spinlock

rust: add `RawSpinLock`

Author: wedsonaf

include/linux/spinlock.h

@@ -99,11 +99,17 @@
   extern void __raw_spin_lock_init(raw_spinlock_t *lock, const char *name,
 				   struct lock_class_key *key, short inner);
 
+static inline void _raw_spin_lock_init(raw_spinlock_t *lock, const char *name,
+				       struct lock_class_key *key)
+{
+	__raw_spin_lock_init(lock, name, key, LD_WAIT_SPIN);
+}
+
 # define raw_spin_lock_init(lock)					\
 do {									\
 	static struct lock_class_key __key;				\
 									\
-	__raw_spin_lock_init((lock), #lock, &__key, LD_WAIT_SPIN);	\
+	_raw_spin_lock_init((lock), #lock, &__key);			\
 } while (0)
 
 #else

rust/helpers.c

@@ -228,6 +228,44 @@ void rust_helper_spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags)
 }
 EXPORT_SYMBOL_GPL(rust_helper_spin_unlock_irqrestore);
 
+void rust_helper__raw_spin_lock_init(raw_spinlock_t *lock, const char *name,
+				     struct lock_class_key *key)
+{
+#ifdef CONFIG_DEBUG_SPINLOCK
+	_raw_spin_lock_init(lock, name, key);
+#else
+	raw_spin_lock_init(lock);
+#endif
+}
+EXPORT_SYMBOL_GPL(rust_helper__raw_spin_lock_init);
+
+void rust_helper_raw_spin_lock(raw_spinlock_t *lock)
+{
+	raw_spin_lock(lock);
+}
+EXPORT_SYMBOL_GPL(rust_helper_raw_spin_lock);
+
+void rust_helper_raw_spin_unlock(raw_spinlock_t *lock)
+{
+	raw_spin_unlock(lock);
+}
+EXPORT_SYMBOL_GPL(rust_helper_raw_spin_unlock);
+
+unsigned long rust_helper_raw_spin_lock_irqsave(raw_spinlock_t *lock)
+{
+	unsigned long flags;
+	raw_spin_lock_irqsave(lock, flags);
+	return flags;
+}
+EXPORT_SYMBOL_GPL(rust_helper_raw_spin_lock_irqsave);
+
+void rust_helper_raw_spin_unlock_irqrestore(raw_spinlock_t *lock,
+					    unsigned long flags)
+{
+	raw_spin_unlock_irqrestore(lock, flags);
+}
+EXPORT_SYMBOL_GPL(rust_helper_raw_spin_unlock_irqrestore);
+
 void rust_helper_init_wait(struct wait_queue_entry *wq_entry)
 {
 	init_wait(wq_entry);

rust/kernel/sync.rs

@@ -42,7 +42,7 @@ pub use mutex::Mutex;
 pub use revocable_mutex::{RevocableMutex, RevocableMutexGuard};
 pub use rwsem::RwSemaphore;
 pub use seqlock::{SeqLock, SeqLockReadGuard};
-pub use spinlock::SpinLock;
+pub use spinlock::{RawSpinLock, SpinLock};
 
 /// Safely initialises an object that has an `init` function that takes a name and a lock class as
 /// arguments, examples of these are [`Mutex`] and [`SpinLock`]. Each of them also provides a more

rust/kernel/sync/spinlock.rs

@@ -190,3 +190,166 @@ unsafe impl<T: ?Sized> Lock<DisabledInterrupts> for SpinLock<T> {
         &self.data
     }
 }
+
+/// Safely initialises a [`RawSpinLock`] with the given name, generating a new lock class.
+#[macro_export]
+macro_rules! rawspinlock_init {
+    ($spinlock:expr, $name:literal) => {
+        $crate::init_with_lockdep!($spinlock, $name)
+    };
+}
+
+/// Exposes the kernel's [`raw_spinlock_t`].
+///
+/// It is very similar to [`SpinLock`], except that it is guaranteed not to sleep even on RT
+/// variants of the kernel.
+///
+/// # Examples
+///
+/// ```
+/// # use kernel::prelude::*;
+/// # use kernel::sync::RawSpinLock;
+/// # use core::pin::Pin;
+///
+/// struct Example {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// // Function that acquires the raw spinlock without changing interrupt state.
+/// fn lock_example(value: &RawSpinLock<Example>) {
+///     let mut guard = value.lock();
+///     guard.a = 10;
+///     guard.b = 20;
+/// }
+///
+/// // Function that acquires the raw spinlock and disables interrupts while holding it.
+/// fn lock_irqdisable_example(value: &RawSpinLock<Example>) {
+///     let mut guard = value.lock_irqdisable();
+///     guard.a = 30;
+///     guard.b = 40;
+/// }
+///
+/// // Initialises a raw spinlock and calls the example functions.
+/// pub fn spinlock_example() {
+///     // SAFETY: `rawspinlock_init` is called below.
+///     let mut value = unsafe { RawSpinLock::new(Example { a: 1, b: 2 }) };
+///     // SAFETY: We don't move `value`.
+///     kernel::rawspinlock_init!(unsafe { Pin::new_unchecked(&mut value) }, "value");
+///     lock_example(&value);
+///     lock_irqdisable_example(&value);
+/// }
+/// ```
+///
+/// [`raw_spinlock_t`]: ../../../include/linux/spinlock.h
+pub struct RawSpinLock<T: ?Sized> {
+    spin_lock: Opaque<bindings::raw_spinlock>,
+
+    // Spinlocks are architecture-defined. So we conservatively require them to be pinned in case
+    // some architecture uses self-references now or in the future.
+    _pin: PhantomPinned,
+
+    data: UnsafeCell<T>,
+}
+
+// SAFETY: `RawSpinLock` can be transferred across thread boundaries iff the data it protects can.
+unsafe impl<T: ?Sized + Send> Send for RawSpinLock<T> {}
+
+// SAFETY: `RawSpinLock` serialises the interior mutability it provides, so it is `Sync` as long as
+// the data it protects is `Send`.
+unsafe impl<T: ?Sized + Send> Sync for RawSpinLock<T> {}
+
+impl<T> RawSpinLock<T> {
+    /// Constructs a new raw spinlock.
+    ///
+    /// # Safety
+    ///
+    /// The caller must call [`RawSpinLock::init_lock`] before using the raw spinlock.
+    pub const unsafe fn new(t: T) -> Self {
+        Self {
+            spin_lock: Opaque::uninit(),
+            data: UnsafeCell::new(t),
+            _pin: PhantomPinned,
+        }
+    }
+}
+
+impl<T: ?Sized> RawSpinLock<T> {
+    /// Locks the raw spinlock and gives the caller access to the data protected by it. Only one
+    /// thread at a time is allowed to access the protected data.
+    pub fn lock(&self) -> Guard<'_, Self, WriteLock> {
+        let ctx = <Self as Lock<WriteLock>>::lock_noguard(self);
+        // SAFETY: The raw spinlock was just acquired.
+        unsafe { Guard::new(self, ctx) }
+    }
+
+    /// Locks the raw spinlock and gives the caller access to the data protected by it.
+    /// Additionally it disables interrupts (if they are enabled).
+    ///
+    /// When the lock in unlocked, the interrupt state (enabled/disabled) is restored.
+    pub fn lock_irqdisable(&self) -> Guard<'_, Self, DisabledInterrupts> {
+        let ctx = <Self as Lock<DisabledInterrupts>>::lock_noguard(self);
+        // SAFETY: The raw spinlock was just acquired.
+        unsafe { Guard::new(self, ctx) }
+    }
+}
+
+impl<T> CreatableLock for RawSpinLock<T> {
+    type CreateArgType = T;
+
+    unsafe fn new_lock(data: Self::CreateArgType) -> Self {
+        // SAFETY: The safety requirements of `new_lock` also require that `init_lock` be called.
+        unsafe { Self::new(data) }
+    }
+
+    unsafe fn init_lock(
+        self: Pin<&mut Self>,
+        name: &'static CStr,
+        key: *mut bindings::lock_class_key,
+    ) {
+        unsafe { bindings::_raw_spin_lock_init(self.spin_lock.get(), name.as_char_ptr(), key) };
+    }
+}
+
+// SAFETY: The underlying kernel `raw_spinlock_t` object ensures mutual exclusion.
+unsafe impl<T: ?Sized> Lock for RawSpinLock<T> {
+    type Inner = T;
+    type GuardContext = EmptyGuardContext;
+
+    fn lock_noguard(&self) -> EmptyGuardContext {
+        // SAFETY: `spin_lock` points to valid memory.
+        unsafe { bindings::raw_spin_lock(self.spin_lock.get()) };
+        EmptyGuardContext
+    }
+
+    unsafe fn unlock(&self, _: &mut EmptyGuardContext) {
+        // SAFETY: The safety requirements of the function ensure that the raw spinlock is owned by
+        // the caller.
+        unsafe { bindings::raw_spin_unlock(self.spin_lock.get()) };
+    }
+
+    fn locked_data(&self) -> &UnsafeCell<T> {
+        &self.data
+    }
+}
+
+// SAFETY: The underlying kernel `raw_spinlock_t` object ensures mutual exclusion.
+unsafe impl<T: ?Sized> Lock<DisabledInterrupts> for RawSpinLock<T> {
+    type Inner = T;
+    type GuardContext = c_types::c_ulong;
+
+    fn lock_noguard(&self) -> c_types::c_ulong {
+        // SAFETY: `spin_lock` points to valid memory.
+        unsafe { bindings::raw_spin_lock_irqsave(self.spin_lock.get()) }
+    }
+
+    unsafe fn unlock(&self, ctx: &mut c_types::c_ulong) {
+        // SAFETY: The safety requirements of the function ensure that the raw spinlock is owned by
+        // the caller.
+        unsafe { bindings::raw_spin_unlock_irqrestore(self.spin_lock.get(), *ctx) };
+    }
+
+    fn locked_data(&self) -> &UnsafeCell<T> {
+        &self.data
+    }
+}