Re: [PATCH] mm/z3fold.c: Reinitialize zhdr structs after migration

Vitaly Wool
2019-07-15T18:43:31Z

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Den mån 15 juli 2019 6:47 emHenry Burns <henryburns@google.com> skrev:

> z3fold_page_migration() calls memcpy(new_zhdr, zhdr, PAGE_SIZE).
> However, zhdr contains fields that can't be directly coppied over (ex:
> list_head, a circular linked list). We only need to initialize the
> linked lists in new_zhdr, as z3fold_isolate_page() already ensures
> that these lists are empty.
>
> Additionally it is possible that zhdr->work has been placed in a
> workqueue. In this case we shouldn't migrate the page, as zhdr->work
> references zhdr as opposed to new_zhdr.
>
> Fixes: bba4c5f96ce4 ("mm/z3fold.c: support page migration")
> Signed-off-by: Henry Burns <henryburns@google.com>
> ---
> mm/z3fold.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 42ef9955117c..9da471bcab93 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -1352,12 +1352,22 @@ static int z3fold_page_migrate(struct
> address_space *mapping, struct page *newpa
> z3fold_page_unlock(zhdr);
> return -EBUSY;
> }
> + if (work_pending(&zhdr->work)) {
> + z3fold_page_unlock(zhdr);
> + return -EAGAIN;
> + }
> new_zhdr = page_address(newpage);
> memcpy(new_zhdr, zhdr, PAGE_SIZE);
> newpage->private = page->private;
> page->private = 0;
> z3fold_page_unlock(zhdr);
> spin_lock_init(&new_zhdr->page_lock);
> + INIT_WORK(&new_zhdr->work, compact_page_work);
> + /*
> + * z3fold_page_isolate() ensures that this list is empty, so we
> only
> + * have to reinitialize it.
> + */
>

On the nitpicking side, we seem to have ensured that directly in migrate :)
Looks OK to me otherwise.

~Vitaly

+ INIT_LIST_HEAD(&new_zhdr->buddy);
> new_mapping = page_mapping(page);
> __ClearPageMovable(page);
> ClearPagePrivate(page);
> --
> 2.22.0.510.g264f2c817a-goog
>
>

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