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

From: Boqun Feng <[email-masked]>
Date: Thu, 7 Nov 2024 12:19:47 -0800

On Thu, Nov 07, 2024 at 05:32:23PM +0100, Eder Zulian wrote:
> 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.
> 
> Introduce __spin_lock_init() to initialize a spin lock with lockdep
> rquired information for PREEMPT_RT builds, and use it in the Rust
> helper.
> 
> Fixes: d2d6422f8bd1 ("x86: Allow to enable PREEMPT_RT.")
> Reported-by: kernel test robot <[email-masked]>
> Closes: https://lore.kernel.org/oe-kbuild-all/[email-masked]/
> Signed-off-by: Eder Zulian <[email-masked]>

Reviewed-by: Boqun Feng <[email-masked]>

For testing, I used the following command as a reproducer:

ARM64:

./tools/testing/kunit/kunit.py run --make_options LLVM=1 --arch arm64 --kconfig_add CONFIG_RUST=y --kconfig_add CONFIG_SMP=y  rust_doctests_kernel --kconfig_add CONFIG_WERROR=y --kconfig_add CONFIG_EXPERT=y --kconfig_add CONFIG_PREEMPT_RT=y --kconfig_add CONFIG_PROVE_LOCKING=y

X86_64:

./tools/testing/kunit/kunit.py run --make_options LLVM=1 --arch arm64 --kconfig_add CONFIG_RUST=y --kconfig_add CONFIG_SMP=y  rust_doctests_kernel --kconfig_add CONFIG_WERROR=y --kconfig_add CONFIG_EXPERT=y --kconfig_add CONFIG_PREEMPT_RT=y --kconfig_add CONFIG_PROVE_LOCKING=y

And I applied this onto the tip/locking/core, can confirm the build
errors are gone. So

Tested-by: Boqun Feng <[email-masked]>

Regards,
Boqun

> ---
> V1 -> V2: Cleaned up style and addressed review comments
> V2 -> V3: Improved commit title and description and corrected the 'Fixed:'
> tag as per reviewer's suggestion
> 
>  include/linux/spinlock_rt.h | 15 +++++++--------
>  rust/helpers/spinlock.c     |  8 ++++++--
>  2 files changed, 13 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/spinlock_rt.h b/include/linux/spinlock_rt.h
> index f9f14e135be7..f6499c37157d 100644
> --- a/include/linux/spinlock_rt.h
> +++ b/include/linux/spinlock_rt.h
> @@ -16,22 +16,21 @@ static inline void __rt_spin_lock_init(spinlock_t *lock, const char *name,
>  }
>  #endif
>  
> -#define spin_lock_init(slock)					\
> +#define __spin_lock_init(slock, name, key, percpu)		\
>  do {								\
> -	static struct lock_class_key __key;			\
> -								\
>  	rt_mutex_base_init(&(slock)->lock);			\
> -	__rt_spin_lock_init(slock, #slock, &__key, false);	\
> +	__rt_spin_lock_init(slock, name, key, percpu);		\
>  } while (0)
>  
> -#define local_spin_lock_init(slock)				\
> +#define _spin_lock_init(slock, percpu)				\
>  do {								\
>  	static struct lock_class_key __key;			\
> -								\
> -	rt_mutex_base_init(&(slock)->lock);			\
> -	__rt_spin_lock_init(slock, #slock, &__key, true);	\
> +	__spin_lock_init(slock, #slock, &__key, percpu);	\
>  } while (0)
>  
> +#define spin_lock_init(slock)		_spin_lock_init(slock, false)
> +#define local_spin_lock_init(slock)	_spin_lock_init(slock, true)
> +
>  extern void rt_spin_lock(spinlock_t *lock) __acquires(lock);
>  extern void rt_spin_lock_nested(spinlock_t *lock, int subclass)	__acquires(lock);
>  extern void rt_spin_lock_nest_lock(spinlock_t *lock, struct lockdep_map *nest_lock) __acquires(lock);
> diff --git a/rust/helpers/spinlock.c b/rust/helpers/spinlock.c
> index b7b0945e8b3c..5971fdf6f755 100644
> --- a/rust/helpers/spinlock.c
> +++ b/rust/helpers/spinlock.c
> @@ -6,10 +6,14 @@ void rust_helper___spin_lock_init(spinlock_t *lock, const char *name,
>  				  struct lock_class_key *key)
>  {
>  #ifdef CONFIG_DEBUG_SPINLOCK
> +# if defined(CONFIG_PREEMPT_RT)
> +	__spin_lock_init(lock, name, key, false);
> +# else /*!CONFIG_PREEMPT_RT */
>  	__raw_spin_lock_init(spinlock_check(lock), name, key, LD_WAIT_CONFIG);
> -#else
> +# endif /* CONFIG_PREEMPT_RT */
> +#else /* !CONFIG_DEBUG_SPINLOCK */
>  	spin_lock_init(lock);
> -#endif
> +#endif /* CONFIG_DEBUG_SPINLOCK */
>  }
>  
>  void rust_helper_spin_lock(spinlock_t *lock)
> -- 
> 2.47.0
>