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

[Linus Torvalds]

On Thu, 23 Apr 2026 at 14:28, Linus Torvalds
<torvalds at linux-foundation.org> wrote:
>
> This is all 100% on the RSEQ kernel code, not on users who took advantage of it.

Side note: when RSEQ was merged, the *primary* documented use case was
literally user space allocators with percpu caches. That's what I was
told at the time.

Now I think it was jemalloc(), not tcmalloc, but it's not like
tcmalloc is some odd minor use-case.

We are pretty much talking about the raison d'être of the whole rseq
feature, not some odd small corner case.

               Linus