[RFC PATCH] mm: Fetch the dirty bit before we reset the pte

[Linus Torvalds]

On Thu, Oct 8, 2020 at 2:27 AM Aneesh Kumar K.V
<aneesh.kumar at linux.ibm.com> wrote:
>
> In copy_present_page, after we mark the pte non-writable, we should
> check for previous dirty bit updates and make sure we don't lose the dirty
> bit on reset.

No, we'll just remove that entirely.

Do you have a test-case that shows a problem? I have a patch that I
was going to delay until 5.10 because I didn't think it mattered in
practice..

The second part of this patch would be to add a sequence count
protection to fast-GUP pinning, so that GUP and fork() couldn't race,
but I haven't written that part.

Here's the first patch anyway. If you actually have a test-case where
this matters, I guess I need to apply it now..

                   Linus
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