[PATCH] rust: xarray: fix false positive lockdep warnings

[Andreas Hindborg <a.hindborg@kernel.org>]

Replace the `xa_init_flags` helper with direct initialization of XArray
structures using `__spin_lock_init`. This allows each XArray to have
its own lock class key for lockdep, preventing false positive warnings
about lock ordering violations.

Add a `new_xarray!` macro that automatically generates a unique lock
class key for each XArray instantiation site. The macro accepts an
optional name parameter and uses the `optional_name!` and
`static_lock_class!` macros to generate appropriate names and lock
classes.

Update the `XArray::new` method signature to accept explicit name and
lock class key parameters. This enables proper lockdep tracking while
maintaining flexibility for advanced use cases.

Remove `rust_helper_xa_init_flags` as it is now dead code.

This was previously part of the series at [1]

Link: https://lore.kernel.org/r/20251203-xarray-entry-send-v1-0-9e5ffd5e3cf0@kernel.org [1]
Fixes: 210b81578efbe ("rust: xarray: Add an abstraction for XArray")
Acked-by: Tamir Duberstein <tamird@gmail.com>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/helpers/xarray.c |  5 -----
 rust/kernel/xarray.rs | 43 +++++++++++++++++++++++++++++++++++++------
 2 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/rust/helpers/xarray.c b/rust/helpers/xarray.c
index 60b299f11451d..644b8b35b1bee 100644
--- a/rust/helpers/xarray.c
+++ b/rust/helpers/xarray.c
@@ -7,11 +7,6 @@ int rust_helper_xa_err(void *entry)
 	return xa_err(entry);
 }
 
-void rust_helper_xa_init_flags(struct xarray *xa, gfp_t flags)
-{
-	return xa_init_flags(xa, flags);
-}
-
 int rust_helper_xa_trylock(struct xarray *xa)
 {
 	return xa_trylock(xa);
diff --git a/rust/kernel/xarray.rs b/rust/kernel/xarray.rs
index a49d6db288458..62a2b2ebfb0bf 100644
--- a/rust/kernel/xarray.rs
+++ b/rust/kernel/xarray.rs
@@ -8,11 +8,31 @@
     alloc, bindings, build_assert,
     error::{Error, Result},
     ffi::c_void,
+    str::CStr,
+    sync::LockClassKey,
     types::{ForeignOwnable, NotThreadSafe, Opaque},
 };
-use core::{iter, marker::PhantomData, pin::Pin, ptr::NonNull};
+use core::{
+    iter,
+    marker::PhantomData,
+    pin::Pin,
+    ptr::{null_mut, NonNull},
+};
 use pin_init::{pin_data, pin_init, pinned_drop, PinInit};
 
+/// Creates a [`XArray`] initialiser with the given name and a newly-created lock class.
+///
+/// It uses the name if one is given, otherwise it generates one based on the file name and line
+/// number.
+#[macro_export]
+macro_rules! new_xarray {
+    ($kind:expr $(, $name:literal)? $(,)?) => {
+        $crate::xarray::XArray::new(
+            $kind, $crate::optional_name!($($name)?), $crate::static_lock_class!())
+    };
+}
+pub use new_xarray;
+
 /// An array which efficiently maps sparse integer indices to owned objects.
 ///
 /// This is similar to a [`crate::alloc::kvec::Vec<Option<T>>`], but more efficient when there are
@@ -27,9 +47,10 @@
 ///
 /// ```rust
 /// use kernel::alloc::KBox;
-/// use kernel::xarray::{AllocKind, XArray};
+/// use kernel::xarray::{new_xarray, AllocKind, XArray};
 ///
-/// let xa = KBox::pin_init(XArray::new(AllocKind::Alloc1), GFP_KERNEL)?;
+/// let xa: Pin<KBox<XArray<KBox<u32>>>> =
+///     KBox::pin_init(new_xarray!(AllocKind::Alloc1), GFP_KERNEL)?;
 ///
 /// let dead = KBox::new(0xdead, GFP_KERNEL)?;
 /// let beef = KBox::new(0xbeef, GFP_KERNEL)?;
@@ -86,7 +107,11 @@ pub enum AllocKind {
 
 impl<T: ForeignOwnable> XArray<T> {
     /// Creates a new initializer for this type.
-    pub fn new(kind: AllocKind) -> impl PinInit<Self> {
+    pub fn new(
+        kind: AllocKind,
+        name: &'static CStr,
+        key: Pin<&'static LockClassKey>,
+    ) -> impl PinInit<Self> {
         let flags = match kind {
             AllocKind::Alloc => bindings::XA_FLAGS_ALLOC,
             AllocKind::Alloc1 => bindings::XA_FLAGS_ALLOC1,
@@ -95,8 +120,14 @@ pub fn new(kind: AllocKind) -> impl PinInit<Self> {
             // SAFETY: `xa` is valid while the closure is called.
             //
             // INVARIANT: `xa` is initialized here to an empty, valid [`bindings::xarray`].
-            xa <- Opaque::ffi_init(|xa| unsafe {
-                bindings::xa_init_flags(xa, flags)
+            xa <- Opaque::ffi_init(|xa: *mut bindings::xarray| unsafe {
+                bindings::__spin_lock_init(
+                    &raw mut (*xa).xa_lock,
+                    name.as_ptr().cast(),
+                    key.as_ptr(),
+                );
+                (*xa).xa_flags = flags;
+                (*xa).xa_head = null_mut();
             }),
             _p: PhantomData,
         })

---
base-commit: 18f7fcd5e69a04df57b563360b88be72471d6b62
change-id: 20260206-xarray-lockdep-fix-10f1cc68e5d7

Best regards,
-- 
Andreas Hindborg <a.hindborg@kernel.org>