On Thu, Jan 7, 2021 at 12:17 PM Linus Torvalds
[off-list ref] wrote:

I still think the real fix is "Don't do that then", and just take the
write lock.

The alternative, of course, is to just make sure the page table flush
is done inside the page table lock (and then we make COW do the copy
inside of it).

But this whole "we know UFFD breaks all rules, we'll add even more
crap to it" approach is horrendous.

               Linus