On 06/27, Paul E. McKenney wrote:
>
> On Wed, Jun 28, 2006 at 01:13:58AM +0400, Oleg Nesterov wrote:
> >
> > Also, I can't understand the purpose of 2-nd synchronize_sched() in
> > synchronize_srcu().
>
> This one handles the srcu_read_unlock() analog of the situation you
> are worried about above. The reader does not have memory barriers in
> srcu_read_unlock(), so an access to the data structure might get
> reordered to follow the decrement of .c[0] -- which would get messed
> up by the following kfree().
Aha, I see.
The last question. The 'srcu-2' you posted today does synchronize_srcu_flip()
twice. You did it this way because srcu is optimized for readers, otherwise we
could just add smp_rmb() into srcu_read_lock() - this should solve the problem
as well.
Is my understanding correct?
Thanks!
Oleg.
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