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

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Message-ID: <87fr7yu6x8.fsf@t14s.mail-host-address-is-not-set>
Date: Wed, 21 Jan 2026 20:01:07 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Gary Guo <gary@...yguo.net>, 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

"Gary Guo" <gary@...yguo.net> writes:

> 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.

My intuition about this was that when the C static function is inlined, a
new static address is used for each place the function is inlined. Is
this not correct?


Best regards,
Andreas Hindborg