linux-kernel - [tip: locking/core] rust: sync: Add lock::Backend::assert_is

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Message-ID: <173506642015.399.4541644660383039585.tip-bot2@tip-bot2>
Date: Tue, 24 Dec 2024 18:53:40 -0000
From: "tip-bot2 for Lyude Paul" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Lyude Paul <lyude@...hat.com>, Boqun Feng <boqun.feng@...il.com>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: locking/core] rust: sync: Add lock::Backend::assert_is_held()

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     fbd7a5a0359bc770e898d918d84977ea61163aad
Gitweb:        https://git.kernel.org/tip/fbd7a5a0359bc770e898d918d84977ea61163aad
Author:        Lyude Paul <lyude@...hat.com>
AuthorDate:    Mon, 25 Nov 2024 15:40:58 -05:00
Committer:     Boqun Feng <boqun.feng@...il.com>
CommitterDate: Thu, 19 Dec 2024 14:04:42 -08:00

rust: sync: Add lock::Backend::assert_is_held()

Since we've exposed Lock::from_raw() and Guard::new() publically, we
want to be able to make sure that we assert that a lock is actually held
when constructing a Guard for it to handle instances of unsafe
Guard::new() calls outside of our lock module.

Hence add a new method assert_is_held() to Backend, which uses lockdep
to check whether or not a lock has been acquired. When lockdep is
disabled, this has no overhead.

[Boqun: Resolve the conflicts with exposing Guard::new(), reword the
 commit log a bit and format "unsafe { <statement>; }" into "unsafe {
 <statement> }" for the consistency. ]

Signed-off-by: Lyude Paul <lyude@...hat.com>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
Link: https://lore.kernel.org/r/20241125204139.656801-1-lyude@redhat.com
---
 rust/helpers/mutex.c              |  5 +++++
 rust/helpers/spinlock.c           |  5 +++++
 rust/kernel/sync/lock.rs          | 10 ++++++++++
 rust/kernel/sync/lock/mutex.rs    |  5 +++++
 rust/kernel/sync/lock/spinlock.rs |  5 +++++
 5 files changed, 30 insertions(+)

diff --git a/rust/helpers/mutex.c b/rust/helpers/mutex.c
index 7e00680..0657555 100644
--- a/rust/helpers/mutex.c
+++ b/rust/helpers/mutex.c
@@ -12,3 +12,8 @@ void rust_helper___mutex_init(struct mutex *mutex, const char *name,
 {
 	__mutex_init(mutex, name, key);
 }
+
+void rust_helper_mutex_assert_is_held(struct mutex *mutex)
+{
+	lockdep_assert_held(mutex);
+}
diff --git a/rust/helpers/spinlock.c b/rust/helpers/spinlock.c
index 5971fdf..42c4bf0 100644
--- a/rust/helpers/spinlock.c
+++ b/rust/helpers/spinlock.c
@@ -30,3 +30,8 @@ int rust_helper_spin_trylock(spinlock_t *lock)
 {
 	return spin_trylock(lock);
 }
+
+void rust_helper_spin_assert_is_held(spinlock_t *lock)
+{
+	lockdep_assert_held(lock);
+}
diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index 72dbf3f..eb80048 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -90,6 +90,13 @@ pub unsafe trait Backend {
         // SAFETY: The safety requirements ensure that the lock is initialised.
         *guard_state = unsafe { Self::lock(ptr) };
     }
+
+    /// Asserts that the lock is held using lockdep.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure that [`Backend::init`] has been previously called.
+    unsafe fn assert_is_held(ptr: *mut Self::State);
 }
 
 /// A mutual exclusion primitive.
@@ -235,6 +242,9 @@ impl<'a, T: ?Sized, B: Backend> Guard<'a, T, B> {
     ///
     /// The caller must ensure that it owns the lock.
     pub unsafe fn new(lock: &'a Lock<T, B>, state: B::GuardState) -> Self {
+        // SAFETY: The caller can only hold the lock if `Backend::init` has already been called.
+        unsafe { B::assert_is_held(lock.state.get()) };
+
         Self {
             lock,
             state,
diff --git a/rust/kernel/sync/lock/mutex.rs b/rust/kernel/sync/lock/mutex.rs
index 10a70c0..70cadbc 100644
--- a/rust/kernel/sync/lock/mutex.rs
+++ b/rust/kernel/sync/lock/mutex.rs
@@ -134,4 +134,9 @@ unsafe impl super::Backend for MutexBackend {
             None
         }
     }
+
+    unsafe fn assert_is_held(ptr: *mut Self::State) {
+        // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
+        unsafe { bindings::mutex_assert_is_held(ptr) }
+    }
 }
diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
index 081c022..ab2f8d0 100644
--- a/rust/kernel/sync/lock/spinlock.rs
+++ b/rust/kernel/sync/lock/spinlock.rs
@@ -133,4 +133,9 @@ unsafe impl super::Backend for SpinLockBackend {
             None
         }
     }
+
+    unsafe fn assert_is_held(ptr: *mut Self::State) {
+        // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
+        unsafe { bindings::spin_assert_is_held(ptr) }
+    }
 }