Re: [PATCH] mm: prevent VMA generation reuse from skipping readers

[Lorenzo Stoakes (ARM)]

-schlopper.

On Thu, Oct 15, 2026 at 05:28:00PM +0100, Lorenzo Stoakes (ARM) wrote:
> On Thu, Oct 15, 2026 at 11:37:35PM +0900, <schlopper> wrote:
> > Both values are 32-bit. After 2^31 complete mmap write-lock acquisitions,
> > an old VMA stamp can alias the live odd generation. vma_start_write() then
> > returns without waiting for an existing reader.
>
> This is really unclear, I guess, as before, a member of the core team (likely
> me) will assess this to see if there's anything actually valid here.

OK I've assessed it, it's at least theoretically possible (Liam, wisely, raised
this before and we all, unwisely, dismissed it so, humble pie time :)

I am working on a patch. It's not necessary to add a new field to VMAs.

Will send out in a little bit.

--
Cheers, Lorenzo