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

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Message-Id: <DFUI6LMASTMK.2WI00LMY5FTSP@garyguo.net>
Date: Wed, 21 Jan 2026 19:10:22 +0000
From: "Gary Guo" <gary@...yguo.net>
To: "Andreas Hindborg" <a.hindborg@...nel.org>, "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>, 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 Jan 21, 2026 at 7:01 PM GMT, Andreas Hindborg wrote:
> "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?

No, the static inside static functions still have the normal static semantics.
There's a single copy regardless how many times the function is inlined.

So you have a unique copy per compilation unit.

Best,
Gary

>
> Best regards,
> Andreas Hindborg