linux-kernel - [PATCH] rust: Add #[must_use] to Lock::try_lock, GlobalLock::try_lock, and XArray::try

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Message-ID: <20250718142026.2232366-1-i@truongsinh.pro>
Date: Fri, 18 Jul 2025 07:20:26 -0700
From: TruongSinh Tran-Nguyen <i@...ongsinh.pro>
To: rust-for-linux@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	ojeda@...nel.org,
	alex.gaynor@...il.com,
	gary@...yguo.net,
	bjorn3_gh@...tonmail.com,
	lossin@...nel.org,
	a.hindborg@...nel.org,
	aliceryhl@...gle.com,
	tmgross@...ch.edu,
	dakr@...nel.org,
	TruongSinh Tran-Nguyen <i@...ongsinh.pro>
Subject: [PATCH] rust: Add #[must_use] to Lock::try_lock, GlobalLock::try_lock, and XArray::try_lock

These methods return an RAII guard that unlocks the lock when dropped.
If the return value is ignored, the lock is released immediately,
which is likely not the intended behavior.

This addresses issue #1133 in the rust-for-linux project.

Signed-off-by: TruongSinh Tran-Nguyen <i@...ongsinh.pro>
---
 rust/kernel/sync/lock.rs        | 1 +
 rust/kernel/sync/lock/global.rs | 1 +
 rust/kernel/xarray.rs           | 1 +
 3 files changed, 3 insertions(+)

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index e82fa5be289c..1c2ddade6d6d 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -175,6 +175,7 @@ pub fn lock(&self) -> Guard<'_, T, B> {
     /// Tries to acquire the lock.
     ///
     /// Returns a guard that can be used to access the data protected by the lock if successful.
+    #[must_use = "the lock unlocks immediately when the guard is unused"]
     pub fn try_lock(&self) -> Option<Guard<'_, T, B>> {
         // SAFETY: The constructor of the type calls `init`, so the existence of the object proves
         // that `init` was called.
diff --git a/rust/kernel/sync/lock/global.rs b/rust/kernel/sync/lock/global.rs
index d65f94b5caf2..fdce038b5e0a 100644
--- a/rust/kernel/sync/lock/global.rs
+++ b/rust/kernel/sync/lock/global.rs
@@ -84,6 +84,7 @@ pub fn lock(&'static self) -> GlobalGuard<B> {
     }
 
     /// Try to lock this global lock.
+    #[must_use = "the lock unlocks immediately when the guard is unused"]
     pub fn try_lock(&'static self) -> Option<GlobalGuard<B>> {
         Some(GlobalGuard {
             inner: self.inner.try_lock()?,
diff --git a/rust/kernel/xarray.rs b/rust/kernel/xarray.rs
index 75719e7bb491..3cca717a3cb4 100644
--- a/rust/kernel/xarray.rs
+++ b/rust/kernel/xarray.rs
@@ -118,6 +118,7 @@ fn iter(&self) -> impl Iterator<Item = NonNull<T::PointedTo>> + '_ {
     }
 
     /// Attempts to lock the [`XArray`] for exclusive access.
+    #[must_use = "the lock unlocks immediately when the guard is unused"]
     pub fn try_lock(&self) -> Option<Guard<'_, T>> {
         // SAFETY: `self.xa` is always valid by the type invariant.
         if (unsafe { bindings::xa_trylock(self.xa.get()) } != 0) {
-- 
2.43.0