Message-Id: <20241219-rust-lockdep-v2-2-f65308fbc5ca@gmail.com>
Date: Thu, 19 Dec 2024 12:58:56 -0800
From: Mitchell Levy <levymitchell0@...il.com>
To: Boqun Feng <boqun.feng@...il.com>, Miguel Ojeda <ojeda@...nel.org>, 
 Alex Gaynor <alex.gaynor@...il.com>, 
 Wedson Almeida Filho <wedsonaf@...il.com>, Gary Guo <gary@...yguo.net>, 
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
 Benno Lossin <benno.lossin@...ton.me>, Alice Ryhl <aliceryhl@...gle.com>, 
 Trevor Gross <tmgross@...ch.edu>, Andreas Hindborg <a.hindborg@...nel.org>, 
 Andreas Hindborg <a.hindborg@...nel.org>
Cc: linux-block@...r.kernel.org, rust-for-linux@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Mitchell Levy <levymitchell0@...il.com>
Subject: [PATCH v2 2/2] rust: lockdep: Use Pin for all LockClassKey usages

Reintroduce dynamically-allocated LockClassKeys such that they are
automatically (de)registered. Require that all usages of LockClassKeys
ensure that they are Pin'd.

Closes: https://github.com/Rust-for-Linux/linux/issues/1102
Suggested-by: Benno Lossin <benno.lossin@...ton.me>
Suggested-by: Boqun Feng <boqun.feng@...il.com>
Signed-off-by: Mitchell Levy <levymitchell0@...il.com>
---
 rust/helpers/helpers.c          |  1 +
 rust/helpers/sync.c             | 13 ++++++++++
 rust/kernel/sync.rs             | 57 ++++++++++++++++++++++++++++++++++++++---
 rust/kernel/sync/condvar.rs     |  5 ++--
 rust/kernel/sync/lock.rs        |  9 +++----
 rust/kernel/sync/lock/global.rs |  5 ++--
 rust/kernel/sync/poll.rs        |  2 +-
 rust/kernel/workqueue.rs        |  3 ++-
 8 files changed, 79 insertions(+), 16 deletions(-)

diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index dcf827a61b52..572af343212c 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -25,6 +25,7 @@
 #include "signal.c"
 #include "slab.c"
 #include "spinlock.c"
+#include "sync.c"
 #include "task.c"
 #include "uaccess.c"
 #include "vmalloc.c"
diff --git a/rust/helpers/sync.c b/rust/helpers/sync.c
new file mode 100644
index 000000000000..ff7e68b48810
--- /dev/null
+++ b/rust/helpers/sync.c
@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/lockdep.h>
+
+void rust_helper_lockdep_register_key(struct lock_class_key *k)
+{
+	lockdep_register_key(k);
+}
+
+void rust_helper_lockdep_unregister_key(struct lock_class_key *k)
+{
+	lockdep_unregister_key(k);
+}
diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
index ae16bfd98de2..13bfdc647c5b 100644
--- a/rust/kernel/sync.rs
+++ b/rust/kernel/sync.rs
@@ -5,6 +5,8 @@
 //! This module contains the kernel APIs related to synchronisation that have been ported or
 //! wrapped for usage by Rust code in the kernel.
 
+use crate::pin_init;
+use crate::prelude::*;
 use crate::types::Opaque;
 
 mod arc;
@@ -22,15 +24,64 @@
 
 /// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
 #[repr(transparent)]
-pub struct LockClassKey(Opaque<bindings::lock_class_key>);
+#[pin_data(PinnedDrop)]
+pub struct LockClassKey {
+    #[pin]
+    inner: Opaque<bindings::lock_class_key>,
+}
 
 // SAFETY: `bindings::lock_class_key` is designed to be used concurrently from multiple threads and
 // provides its own synchronization.
 unsafe impl Sync for LockClassKey {}
 
 impl LockClassKey {
+    /// Initializes a dynamically allocated lock class key. In the common case of using a
+    /// statically allocated lock class key, the static_lock_class! macro should be used instead.
+    ///
+    /// # Example
+    /// ```
+    /// # use kernel::{c_str, stack_pin_init};
+    /// # use kernel::alloc::KBox;
+    /// # use kernel::types::ForeignOwnable;
+    /// # use kernel::sync::{LockClassKey, SpinLock};
+    ///
+    /// let key = KBox::pin_init(LockClassKey::new_dynamic(), GFP_KERNEL)?;
+    /// let key_ptr = key.into_foreign();
+    ///
+    /// // SAFETY: `key_ptr` is returned by the above `into_foreign()`, whose `from_foreign()` has
+    /// // not yet been called.
+    /// stack_pin_init!(let num: SpinLock<u32> = SpinLock::new(
+    ///     0,
+    ///     c_str!("my_spinlock"),
+    ///     unsafe { <Pin<KBox<LockClassKey>> as ForeignOwnable>::borrow(key_ptr) }
+    /// ));
+    ///
+    /// drop(num);
+    ///
+    /// // SAFETY: We dropped `num`, the only use of the key, so the result of the previous
+    /// // `borrow` has also been dropped. Thus, it's safe to use from_foreign.
+    /// unsafe { drop(<Pin<KBox<LockClassKey>> as ForeignOwnable>::from_foreign(key_ptr)) };
+    ///
+    /// # Ok::<(), Error>(())
+    /// ```
+    pub fn new_dynamic() -> impl PinInit<Self> {
+        pin_init!(Self {
+            // SAFETY: lockdep_register_key expects an uninitialized block of memory
+            inner <- Opaque::ffi_init(|slot| unsafe { bindings::lockdep_register_key(slot) })
+        })
+    }
+
     pub(crate) fn as_ptr(&self) -> *mut bindings::lock_class_key {
-        self.0.get()
+        self.inner.get()
+    }
+}
+
+#[pinned_drop]
+impl PinnedDrop for LockClassKey {
+    fn drop(self: Pin<&mut Self>) {
+        // SAFETY: self.as_ptr was registered with lockdep and self is pinned, so the address
+        // hasn't changed. Thus, it's safe to pass to unregister.
+        unsafe { bindings::lockdep_unregister_key(self.as_ptr()) }
     }
 }
 
@@ -43,7 +94,7 @@ macro_rules! static_lock_class {
         // lock_class_key
         static CLASS: $crate::sync::LockClassKey =
             unsafe { ::core::mem::MaybeUninit::uninit().assume_init() };
-        &CLASS
+        $crate::prelude::Pin::static_ref(&CLASS)
     }};
 }
 
diff --git a/rust/kernel/sync/condvar.rs b/rust/kernel/sync/condvar.rs
index 7df565038d7d..29289ccf55cc 100644
--- a/rust/kernel/sync/condvar.rs
+++ b/rust/kernel/sync/condvar.rs
@@ -15,8 +15,7 @@
     time::Jiffies,
     types::Opaque,
 };
-use core::marker::PhantomPinned;
-use core::ptr;
+use core::{marker::PhantomPinned, pin::Pin, ptr};
 use macros::pin_data;
 
 /// Creates a [`CondVar`] initialiser with the given name and a newly-created lock class.
@@ -101,7 +100,7 @@ unsafe impl Sync for CondVar {}
 
 impl CondVar {
     /// Constructs a new condvar initialiser.
-    pub fn new(name: &'static CStr, key: &'static LockClassKey) -> impl PinInit<Self> {
+    pub fn new(name: &'static CStr, key: Pin<&'static LockClassKey>) -> impl PinInit<Self> {
         pin_init!(Self {
             _pin: PhantomPinned,
             // SAFETY: `slot` is valid while the closure is called and both `name` and `key` have
diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index 41dcddac69e2..119e5f569bdb 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -7,12 +7,9 @@
 
 use super::LockClassKey;
 use crate::{
-    init::PinInit,
-    pin_init,
-    str::CStr,
-    types::{NotThreadSafe, Opaque, ScopeGuard},
+    init::PinInit, pin_init, str::CStr, types::NotThreadSafe, types::Opaque, types::ScopeGuard,
 };
-use core::{cell::UnsafeCell, marker::PhantomPinned};
+use core::{cell::UnsafeCell, marker::PhantomPinned, pin::Pin};
 use macros::pin_data;
 
 pub mod mutex;
@@ -121,7 +118,7 @@ unsafe impl<T: ?Sized + Send, B: Backend> Sync for Lock<T, B> {}
 
 impl<T, B: Backend> Lock<T, B> {
     /// Constructs a new lock initialiser.
-    pub fn new(t: T, name: &'static CStr, key: &'static LockClassKey) -> impl PinInit<Self> {
+    pub fn new(t: T, name: &'static CStr, key: Pin<&'static LockClassKey>) -> impl PinInit<Self> {
         pin_init!(Self {
             data: UnsafeCell::new(t),
             _pin: PhantomPinned,
diff --git a/rust/kernel/sync/lock/global.rs b/rust/kernel/sync/lock/global.rs
index 480ee724e3cc..d65f94b5caf2 100644
--- a/rust/kernel/sync/lock/global.rs
+++ b/rust/kernel/sync/lock/global.rs
@@ -13,6 +13,7 @@
 use core::{
     cell::UnsafeCell,
     marker::{PhantomData, PhantomPinned},
+    pin::Pin,
 };
 
 /// Trait implemented for marker types for global locks.
@@ -26,7 +27,7 @@ pub trait GlobalLockBackend {
     /// The backend used for this global lock.
     type Backend: Backend + 'static;
     /// The class for this global lock.
-    fn get_lock_class() -> &'static LockClassKey;
+    fn get_lock_class() -> Pin<&'static LockClassKey>;
 }
 
 /// Type used for global locks.
@@ -270,7 +271,7 @@ impl $crate::sync::lock::GlobalLockBackend for $name {
             type Item = $valuety;
             type Backend = $crate::global_lock_inner!(backend $kind);
 
-            fn get_lock_class() -> &'static $crate::sync::LockClassKey {
+            fn get_lock_class() -> Pin<&'static $crate::sync::LockClassKey> {
                 $crate::static_lock_class!()
             }
         }
diff --git a/rust/kernel/sync/poll.rs b/rust/kernel/sync/poll.rs
index d5f17153b424..c4934f82d68b 100644
--- a/rust/kernel/sync/poll.rs
+++ b/rust/kernel/sync/poll.rs
@@ -89,7 +89,7 @@ pub struct PollCondVar {
 
 impl PollCondVar {
     /// Constructs a new condvar initialiser.
-    pub fn new(name: &'static CStr, key: &'static LockClassKey) -> impl PinInit<Self> {
+    pub fn new(name: &'static CStr, key: Pin<&'static LockClassKey>) -> impl PinInit<Self> {
         pin_init!(Self {
             inner <- CondVar::new(name, key),
         })
diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
index 1dcd53478edd..f8f2f971f985 100644
--- a/rust/kernel/workqueue.rs
+++ b/rust/kernel/workqueue.rs
@@ -369,7 +369,8 @@ unsafe impl<T: ?Sized, const ID: u64> Sync for Work<T, ID> {}
 impl<T: ?Sized, const ID: u64> Work<T, ID> {
     /// Creates a new instance of [`Work`].
     #[inline]
-    pub fn new(name: &'static CStr, key: &'static LockClassKey) -> impl PinInit<Self>
+    #[allow(clippy::new_ret_no_self)]
+    pub fn new(name: &'static CStr, key: Pin<&'static LockClassKey>) -> impl PinInit<Self>
     where
         T: WorkItem<ID>,
     {

-- 
2.34.1

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