linux-kernel - Re: [PATCH 10/10] rust: xarray: fix false positive lockdep warnings

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Message-Id: <DFUE4FBOIF4Z.22DLDSQS06LO4@garyguo.net>
Date: Wed, 21 Jan 2026 15:59:27 +0000
From: "Gary Guo" <gary@...yguo.net>
To: "Andreas Hindborg" <a.hindborg@...nel.org>, "Tamir Duberstein"
 <tamird@...il.com>, "Miguel Ojeda" <ojeda@...nel.org>, "Alex Gaynor"
 <alex.gaynor@...il.com>, "Boqun Feng" <boqun.feng@...il.com>, "Gary Guo"
 <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, "Benno Lossin" <lossin@...nel.org>, "Alice
 Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>, "Danilo
 Krummrich" <dakr@...nel.org>
Cc: "Daniel Gomez" <da.gomez@...nel.org>, <rust-for-linux@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/10] rust: xarray: fix false positive lockdep warnings

On Wed Dec 3, 2025 at 10:26 PM GMT, Andreas Hindborg wrote:
> 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.
>

Isn't this potentially a problem on the C side as well? `xa_init_flags` is a
static inline function, which means that the lock class is going to be the same
if a single C compilation unit initializes multiple xarrays -- unlike when you
use spin_lock_init, where each callsite gets a different lock class.

Best,
Gary

> 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.
>
> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
> ---
>  rust/helpers/xarray.c       |  5 ---
>  rust/kernel/xarray.rs       | 74 +++++++++++++++++++++++++++++++++------------
>  rust/kernel/xarray/entry.rs | 55 ++++++++++++++++++---------------
>  3 files changed, 86 insertions(+), 48 deletions(-)