Re: Patch "asm-generic/bitops/lock.h: Rewrite using atomic_fetch_" causes kernel crash

[Peter Zijlstra]

On Thu, Aug 30, 2018 at 03:23:55PM +0100, Will Deacon wrote:

> Yes, that would be worth trying. However, I also just noticed that the
> fetch-ops (which are now used to implement test_and_set_bit_lock()) seem
> to be missing the backwards branch in the LL/SC case. Yet another diff
> below.
> 
> Will
> 
> --->8
> 
> diff --git a/arch/arc/include/asm/atomic.h b/arch/arc/include/asm/atomic.h
> index 4e0072730241..f06c5ed672b3 100644
> --- a/arch/arc/include/asm/atomic.h
> +++ b/arch/arc/include/asm/atomic.h
> @@ -84,7 +84,7 @@ static inline int atomic_fetch_##op(int i, atomic_t *v)			\
>  	"1:	llock   %[orig], [%[ctr]]		\n"		\
>  	"	" #asm_op " %[val], %[orig], %[i]	\n"		\
>  	"	scond   %[val], [%[ctr]]		\n"		\
> -	"						\n"		\
> +	"	bnz	1b				\n"		\
>  	: [val]	"=&r"	(val),						\
>  	  [orig] "=&r" (orig)						\
>  	: [ctr]	"r"	(&v->counter),					\

ACK!! sorry about that, no idea how I messed that up.

Also, once it all works, they should look at switching to _relaxed
atomics for LL/SC.