On 12/12, Oleg Nesterov wrote:
>
> On 12/11, Srivatsa S. Bhat wrote:
> >
> > IOW, the hotplug readers just increment/decrement their per-cpu refcounts
> > when no writer is active.
>
> plus cli/sti ;) and increment/decrement are atomic.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
OOPS, sorry I was going to say "adds mb()".
And when I look at get_online_cpus_atomic() again it uses rmb(). This
doesn't look correct, we need the full barrier between this_cpu_inc()
and writer_active().
At the same time reader_nested_percpu() can be checked before mb().
Oleg.
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