[REGRESSION] rseq: refactoring in v6.19 broke everyone on arm64 and tcmalloc everywhere

[Linus Torvalds]

On Mon, 27 Apr 2026 at 00:06, Florian Weimer <fweimer at redhat.com> wrote:
>
> RSEQ was intended to be modular

You are entirely missing the point. "Intention" is immaterial.

All that matters is reality. Intentions are ephemeral farts in the wind.

There is *one* major rule in kernel development, and it is "we don't
break user space".

And user space is inconvenient, I know. Users do odd and strange
things. Sometimes on purpose, but quite often entirely accidentally.

The end result is the same as far as the kernel is concerned: we don't
break tools that people use.

This is simply not up for discussion. Any "intent" that isn't actually
enforced by _checking_ for it is only wishful thinking, and worth
nothing at all.

                   Linus