Re: [PATCH mm-hotfixes v2 3/4] mm/ptdump: always stabilise against page table freeing using init_mm

[Kiryl Shutsemau]

On Sun, Jul 12, 2026 at 11:42:26AM +0100, Lorenzo Stoakes wrote:
> x86 and arm64 invoke ptdump_walk_pgd() with non-init_mm mm whilst still
> walking kernel page table ranges.

The code looks good to me.

Same comment as on patch 1 about the commit message structure, only
more so: the race itself is never actually stated -- that these walks
hold only the walked mm's lock, while the freeing exclusion built by
patches 1 and 2 hangs off the init_mm lock. The fact that makes it
possible (x86 shares kernel pgd entries with every mm) is hidden in a
parenthesis. And the last three paragraphs read like v2 changelog
rather than commit message material.

> We take this after mmap write locking the non-init_mm mm. Nothing acquires
> the init_mm lock first before locking an arbitrary mm, so no deadlock is
> possible.

Do we want to document this locking order somewhere?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov