From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-43171.protonmail.ch (mail-43171.protonmail.ch [185.70.43.171]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B33A633AD91 for ; Fri, 29 May 2026 13:40:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.70.43.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780062028; cv=none; b=oODPiwWZBb9/dOiQ2miTugvjTD27r0L8C/5OXvQSHR5XzjD+kjBbns5tbiuozX+jvjZ1so05i1tCbdlYblzu4weWdY0LuPWNSPdH8ZyYjNpUlu+TkuWYckSkjwo64UyuzS0paH4lfAAbSb+//KHqotI7pwKKlViN7Ba1f5TqQrA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780062028; c=relaxed/simple; bh=giXeFeoUiWrc7spHUMsnnZecEIRXFQlqry7Q7BYcCbY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=GkWLMSSA+uEOHRTQhbnChoxGzftzZcx9576K4vK5l62VyvOeqFBGQp/lz8lkZiP2JOJZA7V9aW6TMMqlAIfYZUPEbOrYCZsUDkn00OCrE2GU7Ygh7LDmKYQEv52h6QWGQtMuIuKjRZ59wH7patODIjz6tqmwAT36Oa5R5KL85TQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=onurozkan.dev; spf=pass smtp.mailfrom=onurozkan.dev; dkim=pass (2048-bit key) header.d=onurozkan.dev header.i=@onurozkan.dev header.b=n+pLyoTp; arc=none smtp.client-ip=185.70.43.171 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=onurozkan.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=onurozkan.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=onurozkan.dev header.i=@onurozkan.dev header.b="n+pLyoTp" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=onurozkan.dev; s=protonmail; t=1780062020; x=1780321220; bh=EK7O32EuuqORuh6CzkLMiljHX4OuL+Z/KW00TvctW18=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References:From:To: Cc:Date:Subject:Reply-To:Feedback-ID:Message-ID:BIMI-Selector; b=n+pLyoTpPW+SGy7RjVa0/aCbu/jyqW+/qs1gIMccbugFbkx1ZFvTbO0gBnGrcDtUa +AzFy0XxAyTk9vAWDRRL01pHBN1wvKUqjtgyclbD/ODlPcmqSNjKE/awTfiE1QeErw n46fccifvk61uWjPZWHGWyTaQlP5HAPv3blN4yzLBU4WOQQupgIt9LVzJkOS3svxsx Cn8cqYNBRUbyggQkFMY1zCuUU5kqoOkfU+IQz8of56KizPLMChILRfAQmLx8L6qQdG Wmx2z0v3KenNyLR5q1JXo6vH56QpDioiMO8vmBmfKE8iy/1EsmXKBjZ3hdTFK2opde YFZppIq6OKgRw== X-Pm-Submission-Id: 4gRkxr67rhz1DDL0 From: =?UTF-8?q?Onur=20=C3=96zkan?= To: rcu@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org Cc: ojeda@kernel.org, boqun@kernel.org, gary@garyguo.net, bjorn3_gh@protonmail.com, lossin@kernel.org, a.hindborg@kernel.org, aliceryhl@google.com, tmgross@umich.edu, dakr@kernel.org, peterz@infradead.org, fujita.tomonori@gmail.com, tamird@kernel.org, jiangshanlai@gmail.com, paulmck@kernel.org, josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, =?UTF-8?q?Onur=20=C3=96zkan?= Subject: [PATCH v9 3/4] rust: sync: add SRCU abstraction Date: Fri, 29 May 2026 16:39:53 +0300 Message-ID: <20260529134004.396743-4-work@onurozkan.dev> X-Mailer: git-send-email 2.51.2 In-Reply-To: <20260529134004.396743-1-work@onurozkan.dev> References: <20260529134004.396743-1-work@onurozkan.dev> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Add a Rust abstraction for sleepable RCU (SRCU), backed by C srcu_struct. Provide FFI helpers and a safe wrapper with a guard-based API for read-side critical sections. Cleanup is handled via `PinnedDrop`. It first checks for active read-side sections and emits a warning if any guards were leaked. In that case, it waits in `synchronize_srcu()` rather than risking a UAF by freeing the `srcu_struct` that is still reachable from the C side. It then uses `srcu_barrier()` to drain pending callbacks before finally calling `cleanup_srcu_struct()`. Signed-off-by: Onur Özkan --- rust/kernel/sync.rs | 2 + rust/kernel/sync/srcu.rs | 171 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 173 insertions(+) create mode 100644 rust/kernel/sync/srcu.rs diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs index 993dbf2caa0e..0d6a5f1300c3 100644 --- a/rust/kernel/sync.rs +++ b/rust/kernel/sync.rs @@ -21,6 +21,7 @@ pub mod rcu; mod refcount; mod set_once; +pub mod srcu; pub use arc::{Arc, ArcBorrow, UniqueArc}; pub use completion::Completion; @@ -31,6 +32,7 @@ pub use locked_by::LockedBy; pub use refcount::Refcount; pub use set_once::SetOnce; +pub use srcu::Srcu; /// Represents a lockdep class. /// diff --git a/rust/kernel/sync/srcu.rs b/rust/kernel/sync/srcu.rs new file mode 100644 index 000000000000..723e5e277fd6 --- /dev/null +++ b/rust/kernel/sync/srcu.rs @@ -0,0 +1,171 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Sleepable read-copy update (SRCU) support. +//! +//! C header: [`include/linux/srcu.h`](srctree/include/linux/srcu.h) + +use crate::{ + bindings, + error::to_result, + prelude::*, + sync::LockClassKey, + types::{ + NotThreadSafe, + Opaque, // + }, +}; + +use pin_init::pin_data; + +/// Creates an [`Srcu`] initialiser with the given name and a newly-created lock class. +#[doc(hidden)] +#[macro_export] +macro_rules! new_srcu { + ($($name:literal)?) => { + $crate::sync::Srcu::new($crate::optional_name!($($name)?), $crate::static_lock_class!()) + }; +} +pub use new_srcu; + +/// Sleepable read-copy update primitive. +/// +/// SRCU readers may sleep while holding the read-side guard. +/// +/// The destructor waits for active readers and callbacks, so it may sleep. +/// If a read-side guard has been leaked, dropping an [`Srcu`] may never return. +/// +/// # Invariants +/// +/// This represents a valid `struct srcu_struct` initialized by the C SRCU API +/// and it remains pinned and valid until the pinned destructor runs. +#[repr(transparent)] +#[pin_data(PinnedDrop)] +pub struct Srcu { + #[pin] + inner: Opaque, +} + +impl Srcu { + /// Creates a new SRCU instance. + #[inline] + pub fn new(name: &'static CStr, key: Pin<&'static LockClassKey>) -> impl PinInit { + try_pin_init!(Self { + // INVARIANT: On success, the C initializer creates a valid `srcu_struct` and + // it remains pinned until `PinnedDrop` runs. + inner <- Opaque::try_ffi_init(|ptr: *mut bindings::srcu_struct| { + // SAFETY: `ptr` points to valid uninitialised memory for a `srcu_struct`. + to_result(unsafe { + bindings::init_srcu_struct_with_key(ptr, name.as_char_ptr(), key.as_ptr()) + }) + }), + }) + } + + /// Enters an SRCU read-side critical section. + /// + /// Leaking the returned [`Guard`] leaves the SRCU read-side critical + /// section active and makes `drop` sleep forever. + #[inline] + pub fn read_lock(&self) -> Guard<'_> { + // SAFETY: By the type invariants, `self` contains a valid `struct srcu_struct`. + let idx = unsafe { bindings::srcu_read_lock(self.inner.get()) }; + + // INVARIANT: `idx` was returned by `srcu_read_lock()` for this `Srcu`. + Guard { + srcu: self, + idx, + _not_send: NotThreadSafe, + } + } + + /// Waits until all pre-existing SRCU readers have completed. + #[inline] + pub fn synchronize(&self) { + // SAFETY: By the type invariants, `self` contains a valid `struct srcu_struct`. + unsafe { bindings::synchronize_srcu(self.inner.get()) }; + } + + /// Waits until all pre-existing SRCU readers have completed, expedited. + /// + /// This requests a lower-latency grace period than [`Srcu::synchronize`] typically + /// at the cost of higher system-wide overhead. Prefer [`Srcu::synchronize`] by default + /// and use this variant only when reducing reset or teardown latency is more important + /// than the extra cost. + #[inline] + pub fn synchronize_expedited(&self) { + // SAFETY: By the type invariants, `self` contains a valid `struct srcu_struct`. + unsafe { bindings::synchronize_srcu_expedited(self.inner.get()) }; + } +} + +#[pinned_drop] +impl PinnedDrop for Srcu { + fn drop(self: Pin<&mut Self>) { + let ptr = self.inner.get(); + + if crate::warn_on!( + // SAFETY: By the type invariants, `self` contains a valid and pinned `struct srcu_struct` + // and `srcu_readers_active()` only checks the active reader count. + unsafe { bindings::srcu_readers_active(ptr) } + ) { + // `cleanup_srcu_struct()` may return early if there are still active readers. + // This should only happen if a guard was leaked with `mem::forget`, which is + // "WRONG" code and may cause a UAF because Rust will free the `srcu_struct` + // while it is still referenced from the C side (e.g. by `call_srcu()` callbacks). + // + // Another consequence of leaking guards is that `call_srcu()` callbacks will + // never run because the grace period can never complete due to permanently + // active readers (i.e. leaked guards). + // + // If this ever happens, that means the guard was leaked by mistake and the + // caller must fix the bug. Sleeping here is intentional and less harmful + // than risking a UAF. + // + // SAFETY: By the type invariants, `self` contains a valid and pinned + // `struct srcu_struct`. + unsafe { bindings::synchronize_srcu(ptr) }; + } + + // Ensure all SRCU callbacks have been finished before freeing. + // SAFETY: By the type invariants, `self` contains a valid and pinned `struct srcu_struct`. + unsafe { bindings::srcu_barrier(ptr) }; + + // SAFETY: By the type invariants, `self` contains a valid and pinned `struct srcu_struct`. + unsafe { bindings::cleanup_srcu_struct(ptr) }; + } +} + +// SAFETY: `srcu_struct` may be shared and used across threads. +unsafe impl Send for Srcu {} +// SAFETY: `srcu_struct` may be shared and used concurrently. +unsafe impl Sync for Srcu {} + +/// Guard for an active SRCU read-side critical section on a particular [`Srcu`]. +/// +/// Leaking this guard with [`core::mem::forget`] leaves the SRCU read-side +/// critical section active and makes dropping the associated [`Srcu`] sleep forever. +/// +/// # Invariants +/// +/// `idx` is the index returned by `srcu_read_lock()` for `srcu`. +#[must_use = "if unused, the lock will be immediately unlocked"] +pub struct Guard<'a> { + srcu: &'a Srcu, + idx: i32, + _not_send: NotThreadSafe, +} + +impl Guard<'_> { + /// Explicitly releases the SRCU read-side critical section. + #[inline] + pub fn unlock(self) {} +} + +impl Drop for Guard<'_> { + #[inline] + fn drop(&mut self) { + // SAFETY: `Guard` is only constructible through `Srcu::read_lock()`, + // which returns a valid index for the SRCU instance. + unsafe { bindings::srcu_read_unlock(self.srcu.inner.get(), self.idx) }; + } +} -- 2.51.2