Re: [PATCH] random: use correct memory barriers for crng_node_pool

[Herbert Xu]

On Mon, Sep 21, 2020 at 04:26:39PM -0700, Paul E. McKenney wrote:
>
> > But this reasoning could apply to any data structure that contains
> > a spin lock, in particular ones that are dereferenced through RCU.
> 
> I lost you on this one.  What is special about a spin lock?

I don't know, that was Eric's concern.  He is inferring that
spin locks through lockdep debugging may trigger dependencies
that require smp_load_acquire.

Anyway, my point is if it applies to crng_node_pool then it
would equally apply to RCU in general.

> > So my question if this reasoning is valid, then why aren't we first
> > converting rcu_dereference to use smp_load_acquire?
> 
> For LTO in ARM, rumor has it that Will is doing so.  Which was what
> motivated the BoF on this topic at Linux Plumbers Conference.

Sure, if RCU switches over to smp_load_acquire then I would have
no problems with everybody else following in its footsteps.

Here is the original patch in question:

https://lore.kernel.org/lkml/20200916233042.51634-1-ebiggers@xxxxxxxxxx/

Cheers,
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt