Re: [PATCH v1 06/11] mm: support GUP-triggered unsharing via FAULT_FLAG_UNSHARE (!hugetlb)

[Linus Torvalds]

On Wed, Dec 22, 2021 at 8:08 AM Jan Kara <jack@xxxxxxx> wrote:
>
> Well, but O_DIRECT reads must use FOLL_PIN in any case because they modify
> page data (and so we need to detect them both for COW and filesystem needs).

Well, O_DIRECT reads do, but not necessarily writes.

And hey, even reads have been dodgy in the past when we didn't really
have the pinning logic - there's been a lot of users that just wanted
it to work for their particular use-case rather than in general and in
all situations..

             Linus