Re: [GIT PULL] Add two-byte cmpxchg emulation function for v7.4

[Paul E. McKenney]

On Tue, Oct 20, 2026 at 08:48:32PM +0200, John Paul Adrian Glaubitz wrote:
> Hi Paul,
> 
> On Fri, 2026-10-16 at 20:51 -0700, Paul E. McKenney wrote:
> > However, it sadly does not permit easy implementation of all algorithms
> > needing on two-byte atomic operations because there are some systems still
> > supported by Linux that do not have native two-byte store instructions.
> > There is reason to believe that these systems will soon no longer be
> > supported by Linux.
> 
> Since this paragraph has produced a headline today [1], would you mind
> clarifying what you meant here? What architectures are you talking about?

The important word in the second paragraph quoted by the article is
"systems", which is not "architectures".   To its credit, the article
keeps this straight, but not so much the comments.

And here is Arnd Bergmann's patch that started this:

https://lore.kernel.org/all/20260908152808.3928630-4-arnd@xxxxxxxxxx/

The system Arnd calls out is the Acorn Risc PC, which is one member of the
Arm family.  So not an entire architecture, but rather just a particular
implementation of an architecture, and an old one at that.  Not only
that, but if I remember correctly, Arnd got considerable pushback,
so I am not sure that his support-removal patch is going in just yet,
as in I do not yet see it in -next.

Please feel free to add this as a comment to the article, as the site
is not permitting me to do so.  I have added their feedback email on
CC in case that helps, and in the hope that my doing so does not unduly
annoy them.

							Thanx, Paul

> Thanks,
> Adrian
> 
> > [1] https://www.phoronix.com/news/Linux-7.4-Two-Byte-CMPXCHG
> 
> -- 
>  .''`.  John Paul Adrian Glaubitz
> : :' :  Debian Developer
> `. `'   Physicist
>   `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913