2020-11-06 17:19:17

by Ahmed S. Darwish

Subject: Re: [PATCH v3 2/2] mm: prevent gup_fast from racing with COW during fork

Hi Jason,

On Fri, Nov 06, 2020 at 11:55:14AM -0400, Jason Gunthorpe wrote:
...
> + if (gup_flags & FOLL_PIN) {
> + seq = raw_read_seqcount(&current->mm->write_protect_seq);
> + if (seq & 1)
> + return 0;
> + }
> +
...
> + if (gup_flags & FOLL_PIN) {
> + if (read_seqcount_t_retry(&current->mm->write_protect_seq,
> + seq)) {
> + unpin_user_pages(pages, nr_pinned);
> + return 0;
> + }
> + }

From seqlock.h:

/**
* raw_read_seqcount() - read the raw seqcount_t counter value
* ...
* Return: count to be passed to read_seqcount_retry()
*/
#define raw_read_seqcount(s)

Please avoid using the internal API (read_seqcount_*t*_retry) and just
use read_seqcount_retry() as the documentation suggests.

(I guess you just missed changing that last one... I'm in process of
changing all these "*_seqcount_t_*" stuff to "do_*" as we talked on the
v2 thread. Hopefully there will be no more confusion after that.)

Kind regards,

--
Ahmed S. Darwish
Linutronix GmbH