Re: [PATCH] Detect and warn on atomic_inc/atomic_dec wrappingaround

[Ingo Molnar]

* Nikanth Karthikesan <knikanth@xxxxxxxxxx> wrote:

> Add a debug option to detect and warn when the 32-bit atomic_t 
> wraps around during atomic_inc and atomic_dec.
> 
> Signed-off-by: Nikanth Karthikesan <knikanth@xxxxxxx>

hm, what's the motivation?

As a generic debug helper this is not appropriate i think - counts 
can easily have a meaning when going negative as well. (we have no 
signed-atomic primitives)

>  static inline void atomic_inc(atomic_t *v)
>  {
> +#if defined(CONFIG_ENABLE_WARN_ATOMIC_INC_WRAP)
> +	WARN_ON(atomic_add_unless(v, 1, INT_MAX) == 0);
> +#else
>  	asm volatile(LOCK_PREFIX "incl %0"
>  		     : "+m" (v->counter));
> +#endif
>  }

also looks a bit ugly - this ugly #ifdef would spread into every 
architecture.

If we want to restrict atomic_t value ranges like that then the 
clean solution would be to add generic wrappers doing the debug 
(once, in generic code), and renaming the arch primitives to 
raw_atomic_inc() (etc), doing the lowlevel bits cleanly.

Do we really want this?

	Ingo
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