Re: rcu_read_lock lost its compiler barrier

From: Herbert Xu
Date: Thu Jun 06 2019 - 05:33:19 EST

On Thu, Jun 06, 2019 at 02:06:19AM -0700, Paul E. McKenney wrote:
> Or is your point instead that given the initial value of "a" being
> zero and the value stored to "a" being one, there is no way that
> any possible load and store tearing (your slicing and dicing) could
> possibly mess up the test of the value loaded from "a"?

Exactly. If you can dream up of a scenario where the compiler can
get this wrong I'm all ears.

> > But I do concede that in the general RCU case you must have the
> > READ_ONCE/WRITE_ONCE calls for rcu_dereference/rcu_assign_pointer.
> OK, good that we are in agreement on this part, at least! ;-)

Well only because we're allowing crazy compilers that can turn
a simple word-aligned word assignment (a = b) into two stores.

Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
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