rust: add pr_*_ratelimited! macros for printing

Printing can be very expensive if it occurs often, so printing that can
be triggered by userspace should be rate limited. For this purpose, add
a Rust wrapper around `struct ratelimit_state` and use it in the new
macros.

The new files will fall under the catch-all RUST maintainers entry.

Tested-by: Alvin Sun <alvin.sun@linux.dev>
Reviewed-by: Carlos Llamas <cmllamas@google.com>
Link: https://github.com/Rust-for-Linux/linux/issues/122
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20261007-pr-ratelimited-v6-3-f14accd4ea3b@google.com
[ Removed unused link reference definitions. On the `static`, allowed
  the `non_upper_case_globals` lint so that `kernel` users (and users
  providing their own name) do not warn. Reworded title for typo.
    - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

4 files changed, 210 insertions, 1 deletions

diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 7225abc64084..a4747f75b163 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -120,6 +120,7 @@ pub mod processor;
 pub mod ptr;
 #[cfg(CONFIG_RUST_PWM_ABSTRACTIONS)]
 pub mod pwm;
+pub mod ratelimit;
 pub mod rbtree;
 pub mod regulator;
 pub mod revocable;
diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
index ca396f1f78a6..bcaa232205be 100644
--- a/rust/kernel/prelude.rs
+++ b/rust/kernel/prelude.rs
@@ -107,13 +107,21 @@ pub use super::{
     },
     init::InPlaceInit,
     pr_alert,
+    pr_alert_ratelimited,
     pr_crit,
+    pr_crit_ratelimited,
     pr_debug,
+    pr_debug_ratelimited,
     pr_emerg,
+    pr_emerg_ratelimited,
     pr_err,
+    pr_err_ratelimited,
     pr_info,
+    pr_info_ratelimited,
     pr_notice,
+    pr_notice_ratelimited,
     pr_warn,
+    pr_warn_ratelimited,
     str::CStrExt as _,
     try_init,
     try_pin_init,
diff --git a/rust/kernel/ratelimit.rs b/rust/kernel/ratelimit.rs
new file mode 100644
index 000000000000..2c54099cf11e
--- /dev/null
+++ b/rust/kernel/ratelimit.rs
@@ -0,0 +1,201 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rate limiting support.
+//!
+//! C header: [`include/linux/ratelimit.h`](srctree/include/linux/ratelimit.h)
+
+use crate::{
+    bindings,
+    prelude::*,
+    types::Opaque, //
+};
+
+/// Defines a `static` containing a [`Ratelimit`].
+#[macro_export]
+macro_rules! ratelimit_state_init {
+    ($name:ident, $interval:expr, $burst:expr $(,)?) => {
+        #[allow(non_upper_case_globals)]
+        static $name: $crate::ratelimit::Ratelimit = {
+            let name = $crate::c_str!(::core::stringify!($name));
+            let interval = $interval;
+            let burst = $burst;
+            // SAFETY: This will be stored in static memory.
+            unsafe { $crate::ratelimit::Ratelimit::new_static(name, interval, burst) }
+        };
+    };
+}
+pub use ratelimit_state_init;
+
+/// Rate limiter state.
+///
+/// # Invariants
+///
+/// The `inner` field contains an initialized `struct ratelimit_state`.
+#[pin_data(PinnedDrop)]
+#[repr(transparent)]
+pub struct Ratelimit {
+    #[pin]
+    inner: Opaque<bindings::ratelimit_state>,
+}
+
+// SAFETY: `Ratelimit` is safe to be sent to any task.
+unsafe impl Send for Ratelimit {}
+
+// SAFETY: `Ratelimit` is safe to be accessed concurrently as it is protected by an internal
+// spinlock.
+unsafe impl Sync for Ratelimit {}
+
+impl Ratelimit {
+    /// Constructs a [`Ratelimit`] with the specified configuration.
+    ///
+    /// If `interval` is zero, then no rate limit is applied.
+    #[inline]
+    pub fn new(interval: i32, burst: i32) -> impl PinInit<Self> {
+        // INVARIANT: This creates a `Ratelimit` containing an initialized `struct ratelimit_state`
+        pin_init!(Self {
+            inner <- Opaque::ffi_init(|slot: *mut bindings::ratelimit_state| {
+                // SAFETY: `slot` is a valid pointer to an uninitialized `struct ratelimit_state`.
+                // The memory is pinned so it remains valid until `ratelimit_state_exit` is called.
+                unsafe { bindings::ratelimit_state_init(slot, interval, burst) };
+            }),
+        })
+    }
+
+    /// Constructs a [`Ratelimit`] with the default configuration.
+    #[inline]
+    pub fn new_default() -> impl PinInit<Self> {
+        Ratelimit::new(Ratelimit::DEFAULT_INTERVAL, Ratelimit::DEFAULT_BURST)
+    }
+
+    /// Constructs a [`Ratelimit`] with the specified configuration.
+    ///
+    /// The name will be used for the lockdep name of the internal spinlock. See [`Self::new`] for
+    /// the meaning of `interval` and `burst`.
+    ///
+    /// # Safety
+    ///
+    /// The resulting value must be stored in static memory.
+    #[inline]
+    pub const unsafe fn new_static(name: &'static CStr, interval: i32, burst: i32) -> Self {
+        // INVARIANT: This creates a `Ratelimit` containing an initialized `struct ratelimit_state`.
+        Self {
+            inner: Opaque::new(bindings::ratelimit_state {
+                lock: kernel::sync::lock::spinlock::raw_spin_lock_unlocked(name),
+                interval,
+                burst,
+                ..pin_init::zeroed()
+            }),
+        }
+    }
+
+    /// The default interval used for rate limiting.
+    pub const DEFAULT_INTERVAL: i32 = bindings::DEFAULT_RATELIMIT_INTERVAL as i32;
+
+    /// The default burst size.
+    pub const DEFAULT_BURST: i32 = bindings::DEFAULT_RATELIMIT_BURST as i32;
+
+    /// Check if an action should be rate-limited.
+    ///
+    /// Returns [`true`] if the action is allowed, and [`false`] if it should be suppressed.
+    #[inline]
+    pub fn ratelimit(&self, func: &CStr) -> bool {
+        // SAFETY: `self.inner.get()` is a valid pointer to a `struct ratelimit_state`.
+        // The lifetime of `func` ensures the pointer remains valid for the duration of the call.
+        // The C function `___ratelimit` handles its own internal locking, so it is safe to call
+        // concurrently.
+        unsafe { bindings::___ratelimit(self.inner.get(), func.as_char_ptr()) != 0 }
+    }
+}
+
+#[pinned_drop]
+impl PinnedDrop for Ratelimit {
+    #[inline]
+    fn drop(self: Pin<&mut Self>) {
+        // SAFETY: By the type invariants, this struct contains an initialized `struct
+        // ratelimit_state`.
+        unsafe { bindings::ratelimit_state_exit(self.inner.get()) };
+    }
+}
+
+/// Helper macro to implement ratelimited printing.
+#[macro_export]
+#[doc(hidden)]
+macro_rules! print_ratelimited {
+    ($print_macro:ident, $($arg:tt)*) => {{
+        $crate::ratelimit::ratelimit_state_init!(
+            _rs,
+            $crate::ratelimit::Ratelimit::DEFAULT_INTERVAL,
+            $crate::ratelimit::Ratelimit::DEFAULT_BURST,
+        );
+        let loc = $crate::c_str!(::core::concat!(::core::file!(), ":", ::core::line!()));
+        if $crate::ratelimit::Ratelimit::ratelimit(&_rs, loc) {
+            $crate::$print_macro!($($arg)*);
+        }
+    }};
+}
+
+/// Prints an emergency-level message (level 0) if allowed by a rate limiter.
+#[macro_export]
+macro_rules! pr_emerg_ratelimited (
+    ($($arg:tt)*) => (
+        $crate::print_ratelimited!(pr_emerg, $($arg)*)
+    )
+);
+
+/// Prints an alert-level message (level 1) if allowed by a rate limiter.
+#[macro_export]
+macro_rules! pr_alert_ratelimited (
+    ($($arg:tt)*) => (
+        $crate::print_ratelimited!(pr_alert, $($arg)*)
+    )
+);
+
+/// Prints a critical-level message (level 2) if allowed by a rate limiter.
+#[macro_export]
+macro_rules! pr_crit_ratelimited (
+    ($($arg:tt)*) => (
+        $crate::print_ratelimited!(pr_crit, $($arg)*)
+    )
+);
+
+/// Prints an error-level message (level 3) if allowed by a rate limiter.
+#[macro_export]
+macro_rules! pr_err_ratelimited (
+    ($($arg:tt)*) => (
+        $crate::print_ratelimited!(pr_err, $($arg)*)
+    )
+);
+
+/// Prints a warning-level message (level 4) if allowed by a rate limiter.
+#[macro_export]
+macro_rules! pr_warn_ratelimited (
+    ($($arg:tt)*) => (
+        $crate::print_ratelimited!(pr_warn, $($arg)*)
+    )
+);
+
+/// Prints a notice-level message (level 5) if allowed by a rate limiter.
+#[macro_export]
+macro_rules! pr_notice_ratelimited (
+    ($($arg:tt)*) => (
+        $crate::print_ratelimited!(pr_notice, $($arg)*)
+    )
+);
+
+/// Prints an info-level message (level 6) if allowed by a rate limiter.
+#[macro_export]
+macro_rules! pr_info_ratelimited (
+    ($($arg:tt)*) => (
+        $crate::print_ratelimited!(pr_info, $($arg)*)
+    )
+);
+
+/// Prints a debug-level message (level 7) if allowed by a rate limiter.
+#[macro_export]
+macro_rules! pr_debug_ratelimited (
+    ($($arg:tt)*) => (
+        if cfg!(debug_assertions) {
+            $crate::print_ratelimited!(pr_debug, $($arg)*)
+        }
+    )
+);
diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
index 037fa63ebcac..6a71bb3a5c45 100644
--- a/rust/kernel/sync/lock/spinlock.rs
+++ b/rust/kernel/sync/lock/spinlock.rs
@@ -468,7 +468,6 @@ mod tests {
 ///
 /// For use in statics containing raw spinlocks.
 #[doc(alias("__SPIN_LOCK_UNLOCKED", "DEFINE_SPINLOCK"))]
-#[expect(dead_code)]
 pub(crate) const fn raw_spin_lock_unlocked(name: &'static CStr) -> bindings::raw_spinlock_t {
     // Silence unused variable warnings.
     #[cfg(not(CONFIG_DEBUG_LOCK_ALLOC))]