linux-kernel - Re: [PATCH 01/13] mm: Update ptep_get

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Message-ID: <CAHk-=wjnvPA7mi-E3jVEfCWXCNJNZEUjm6XODbbzGOh9c8mhgw@mail.gmail.com>
Date:   Mon, 31 Oct 2022 10:28:11 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Nadav Amit <nadav.amit@...il.com>, Jann Horn <jannh@...gle.com>,
        John Hubbard <jhubbard@...dia.com>, X86 ML <x86@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        jroedel@...e.de, ubizjak@...il.com,
        Alistair Popple <apopple@...dia.com>
Subject: Re: [PATCH 01/13] mm: Update ptep_get_lockless()s comment

On Mon, Oct 31, 2022 at 2:36 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> >  (c) move it to clean_and_free_pages_and_swap_cache() that actually
> > does the page_zap_pte_rmap() now.
>
> I'm leaning towards (c); simply because the error case is so terrifying
> I feel we should check for it (and I do have vague memories of us
> actually hitting something like this in the very distant past).

Ok. At that point we no longer have the pte or the virtual address, so
it's not goign to be exactly the same debug output.

But I think it ends up being fairly natural to do

        VM_WARN_ON_ONCE_PAGE(page_mapcount(page) < 0, page);

instead, and I've fixed that last patch up to do that.

                      Linus