On Mon, Oct 14, 2013 at 11:05:08AM +0200, Peter Zijlstra wrote:
> On Sat, Oct 12, 2013 at 07:06:56PM +0200, Oleg Nesterov wrote:
> > it even disables irqs, so this should always imply rcu_read_lock() with
> > any implementation,
>
> Not so; I could make an RCU implementation that drives the state machine
> from rcu_read_unlock(). Such an implementation doesn't need the
> interrupt driven poll-state driver we currently have and could thus
> subvert that assumption :-)
>
> Then again, there's a good reason PaulMck didn't pick this
> implementation.
True enough, but there really are some out-of-tree RCU implementations
that do take this approach and where disabling interrupts would not
block preemptible RCU. So please do not rely on this implementation
detail. You never know...
> > In fact I do not even understand why getaffinity() doesn't simply
> > return ->cpus_allowed, but this is off-topic.
>
> Yeah, me neither :-(, it always surprises me. But changing it is likely
> to break stuff so there we are.
I know that feeling...
Thanx, Paul
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