[PATCH v3 0/1] rust: helpers: Avoid raw_spin_lock initialization for PREEMPT_RT

[Eder Zulian <ezulian@redhat.com>]

Hello!

When PREEMPT_RT=y, spin locks are mapped to rt_mutex types, so using
spinlock_check() + __raw_spin_lock_init() to initialize spin locks is
incorrect, and would cause build errors. 

This v3 patch introduces __spin_lock_init() to initialize a spin lock with
lockdep rquired information for PREEMPT_RT builds, and use it in the Rust
helper.

This patch was developed on top of linux-next/master.

As a note, at the time of writing, RUST support for x86_64 depends on
!(MITIGATION_RETHUNK && KASAN) || RUSTC_VERSION >= 108300. Miguel Ojeda
pointed out that this can be avoided with Rust 1.83, to be released in 3
weeks (2024-11-28).

In order to reproduce the problem rust must be available on the system.

  $ make LLVM=1 rustavailable

With CONFIG_PREEMPT_RT=y, CONFIG_RUST=y, and CONFIG_DEBUG_SPINLOCK=y a
x86_64 kernel can be built with

  $ make LLVM=1 -j$(nproc) bzImage 

The problem was reported at least in:
https://lore.kernel.org/oe-kbuild-all/202409251238.vetlgXE9-lkp@intel.com/
https://lore.kernel.org/all/20241107182411.57e2b418@canb.auug.org.au/

Links to v1 and v2 where improvement suggestions were made:
https://lore.kernel.org/all/20241014195253.1704625-1-ezulian@redhat.com/
https://lore.kernel.org/all/20241106211215.2005909-1-ezulian@redhat.com/

Version 2 changes:

- Cleaned up style and incorporated feedback from reviewers Boqun Feng and
  Miguel Ojeda.

Version 3 changes:

- Addressed review comments from Boqun Feng. Improved commit title and
  description and used a proper 'Fixed:' tag.

Thanks,

Eder Zulian (1):
  rust: helpers: Avoid raw_spin_lock initialization for PREEMPT_RT

 include/linux/spinlock_rt.h | 15 +++++++--------
 rust/helpers/spinlock.c     |  8 ++++++--
 2 files changed, 13 insertions(+), 10 deletions(-)

-- 
2.47.0