[RFC 12/32] stack: always use C11 memory model implementation

[Morten Brørup]

+TO: x86 maintainers, ThunderX maintainers

> From: Stephen Hemminger [mailto:stephen at networkplumber.org]
> Sent: Wednesday, 29 July 2026 19.54
> 
> The generic and C11 lock-free stack implementations differ only in
> memory ordering. The generic version uses a full barrier where its
> own comments state an acquire fence is sufficient, and seq_cst for
> all length counter operations.
> 
> Only x86 and ThunderX still used the generic version. On x86 the
> switch removes a locked add per CAS attempt in push and pop; TSO
> provides the acquire semantics. On ThunderX the pop fence weakens
> from dmb ish to dmb ishld and the push fence goes away. Unlike the
> ring, no platform selected the generic stack for measured
> performance reasons.
> 
> Remove it and use the C11 implementation everywhere.

The lack of measured performance difference documentation is not a valid reason to remove the generic version!

It would be reasonable to assume that x86 (and ThunderX) use the generic version for non-insignificant performance reasons.

If there is no performance difference, I agree with this patch. Otherwise not.
This could be verified by providing the missing measurements.