[v2] powerpc: spinlock: Fix spin_unlock_wait()

[Michael Ellerman]

On Fri, 2016-03-06 at 03:49:48 UTC, Boqun Feng wrote:
> diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h
> index 523673d7583c..2ed893662866 100644
> --- a/arch/powerpc/include/asm/spinlock.h
> +++ b/arch/powerpc/include/asm/spinlock.h
> @@ -64,6 +64,25 @@ static inline int arch_spin_is_locked(arch_spinlock_t *lock)
>  }
>  
>  /*
> + * Use a ll/sc loop to read the lock value, the STORE part of this operation is
> + * used for making later lock operation observe it.
> + */
> +static inline bool arch_spin_is_locked_sync(arch_spinlock_t *lock)
> +{
> +	arch_spinlock_t tmp;
> +
> +	__asm__ __volatile__(
> +"1:	" PPC_LWARX(%0, 0, %2, 1) "\n"

As discussed offline I think we want to use EH=0 here (the final parameter).

>From the ISA:

  The value of EH provides a hint as to whether the program will perform a
  subsequent store to the word in storage addressed by EA before some other
  processor attempts to modify it.

  0 Other programs might attempt to modify the word in storage addressed by EA
    regardless of the result of the corresponding stwcx. instruction.

cheers