[ofa-general] Re: [patch 02/10] emm: notifier logic

[Christoph Lameter]

On Sat, 5 Apr 2008, Andrea Arcangeli wrote:

> > +	rcu_assign_pointer(mm->emm_notifier, e);
> > +	mm_unlock(mm);
> 
> My mm_lock solution makes all rcu serialization an unnecessary
> overhead so you should remove it like I already did in #v11. If it
> wasn't the case, then mm_lock wouldn't be a definitive fix for the
> race.

There still could be junk in the cache of one cpu. If you just read the 
new pointer but use the earlier content pointed to then you have a 
problem.

So a memory fence / barrier is needed to guarantee that the contents 
pointed to are fetched after the pointer.