Re: [RFC] Bridging the gap between the Linux Kernel Memory Consistency Model (LKMM) and C11/C++11 atomics

[Paul E. McKenney]

On Tue, Jul 04, 2023 at 04:25:45PM -0400, Alan Stern wrote:
> On Tue, Jul 04, 2023 at 01:19:23PM -0400, Olivier Dion wrote:

[ . . . ]

> > I am puzzled by this.  Initialization of a shared variable does not need
> > to be atomic until its publication.  Could you expand on this?
> 
> In the kernel, I believe it sometimes happens that an atomic variable 
> may be published before it is initialized.  (If that's wrong, Paul or 
> Peter can correct me.)  But since this doesn't apply to the situations 
> you're concerned with, you can forget I mentioned it.

Both use cases exist.

A global atomic is implicitly published at compile time.  If the desired
initial value is not known until multiple threads are running, then it
is necessary to be careful.  Hence double-check locking and its various
replacements.  (Clearly, if you can determine the initial value before
going multithreaded, life is simpler.)

And dynamically allocated or on-stack storage is the other case, where
there is a point in time when the storage is private even after multiple
threads are running.

Or am I missing the point?

							Thanx, Paul