Re: [PATCH 01/13] mm: Update ptep_get_lockless()s comment

[Linus Torvalds]

On Sat, Oct 29, 2022 at 1:15 PM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> I can think of three options:
>
>  (a) filesystems just deal with it
>
>  (b) we could move the "page_remove_rmap()" into the "flush-and-free" path too
>
>  (c) we could actually add a spinlock (hashed on the page?) for this
>
> I think (a) is basically our current expectation.

Side note: anybody doing gup + set_page_dirty() won't be fixed by b/c
anyway, so I think (a) is basically the only thing.

And that's true even if you do a page pinning gup, since the source of
the gup may be actively unmapped after the gup.

So a filesystem that thinks that only write, or a rmap-accessible mmap
can turn the page dirty really seems to be fundamentally broken.

And I think that has always been the case, it's just that filesystem
writers may not have been happy with it, and may not have had
test-cases for it.

It's not surprising that the filesystem people then try to blame users.

          Linus