Re: [PATCH 03/20] mmiowb: Hook up mmiowb helpers to spinlocks and generic I/O accessors

[Nicholas Piggin]

Will Deacon's on March 2, 2019 12:03 am:
> @@ -177,6 +178,7 @@ do {								\
>  static inline void do_raw_spin_lock(raw_spinlock_t *lock) __acquires(lock)
>  {
>  	__acquire(lock);
> +	mmiowb_spin_lock();
>  	arch_spin_lock(&lock->raw_lock);
>  }
>  
> @@ -188,16 +190,23 @@ static inline void
>  do_raw_spin_lock_flags(raw_spinlock_t *lock, unsigned long *flags) __acquires(lock)
>  {
>  	__acquire(lock);
> +	mmiowb_spin_lock();
>  	arch_spin_lock_flags(&lock->raw_lock, *flags);
>  }

You'd be better to put these inside the spin lock, to match your 
trylock.

Also it means the mmiowb state can be used inside a lock/unlock pair
without a compiler barrer forcing it to be reloaded, should be better
code generation for very small critical sections on archs which inline
lock and unlock.

>  
>  static inline int do_raw_spin_trylock(raw_spinlock_t *lock)
>  {
> -	return arch_spin_trylock(&(lock)->raw_lock);
> +	int ret = arch_spin_trylock(&(lock)->raw_lock);
> +
> +	if (ret)
> +		mmiowb_spin_lock();
> +
> +	return ret;
>  }
>  
>  static inline void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock)
>  {
> +	mmiowb_spin_unlock();
>  	arch_spin_unlock(&lock->raw_lock);
>  	__release(lock);
>  }

Thanks,
Nick