RFC: mutex: hung tasks on SMP platforms with asm-generic/mutex-xchg.h

[Peter Zijlstra]

On Thu, 2012-08-09 at 12:57 -0400, Nicolas Pitre wrote:
> 
> In other words, I think this should look like this:
> 
> diff --git a/include/asm-generic/mutex-xchg.h b/include/asm-generic/mutex-xchg.h
> index 580a6d35c7..44a66c99c8 100644
> --- a/include/asm-generic/mutex-xchg.h
> +++ b/include/asm-generic/mutex-xchg.h
> @@ -25,8 +25,11 @@
>  static inline void
>  __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
>  {
> -       if (unlikely(atomic_xchg(count, 0) != 1))
> -               fail_fn(count);
> +       if (unlikely(atomic_xchg(count, 0) != 1)) {
> +               /* Mark lock contention explicitly */
> +               if (likely(atomic_xchg(count, -1) != 1))
> +                       fail_fn(count);
> +       }
>  } 

OK, I like this.. Thanks guys! Will will you send a final and complete
patch?