[ltt-dev] [PATCH 1/3] Fix the "unknown" case

[pbonzini@redhat.com (Paolo Bonzini)]

On 06/14/2010 02:41 AM, Paul E. McKenney wrote:
> The compiler (and sometimes the CPU) are within their rights to move
> code into a lock-based critical section.  With two
> locks:
>
> 	do_first_thing();
> 	acquire_lock();
> 	release_lock();
> 	acquire_lock();
> 	release_lock();
> 	do_second_thing();
>
> the worst that the compiler and CPU can do is:
>
> 	acquire_lock();
> 	do_first_thing();
> 	release_lock();
> 	acquire_lock();
> 	do_second_thing();
> 	release_lock();
>
> which is still acting like a memory barrier.

Interesting, so it's actually the release+acquire that is doing the job. 
  I thought about barrier+acquire+release+barrier, but that would 
placate the compiler only, not the CPU.

Paolo