Re: [RFC] should VM_BUG_ON(cond) really evaluate cond

Andi Kleen
2011-10-28T01:25:29Z

On Fri, Oct 28, 2011 at 03:19:21AM +0200, Eric Dumazet wrote:
> In commit 4e60c86bd9e (gcc-4.6: mm: fix unused but set warnings)
> Andi forced VM_BUG_ON(cond) to evaluate cond, even if CONFIG_DEBUG_VM is
> not set :
>
> #ifdef CONFIG_DEBUG_VM
> #define VM_BUG_ON(cond) BUG_ON(cond)
> #else
> #define VM_BUG_ON(cond) do { (void)(cond); } while (0)
> #endif

Eventually the warnings were disabled in the Makefile.
So it would be reasonable to just revert that patch now, at least
for VM_BUG_ON, if it costs performance.

>
> So maybe a fix would be to introduce an atomic_read_stable() variant ?
>
> static inline int atomic_read_stable(const atomic_t *v)
> {
> return v->counter;
> }

Seems reasonable too. In fact we usually should have memory barriers
for this anyways which obsolete the volatile.

-Andi

--
ak@linux.intel.com -- Speaking for myself only.