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SubjectRe: Memory hotplug softlock issue
On Mon 19-11-18 15:10:16, Michal Hocko wrote:
[...]
> In other words. Why cannot we do the following?

Baoquan, this is certainly not the right fix but I would be really
curious whether it makes the problem go away.

> diff --git a/mm/migrate.c b/mm/migrate.c
> index f7e4bfdc13b7..7ccab29bcf9a 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -324,19 +324,9 @@ void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
> goto out;
>
> page = migration_entry_to_page(entry);
> -
> - /*
> - * Once page cache replacement of page migration started, page_count
> - * *must* be zero. And, we don't want to call wait_on_page_locked()
> - * against a page without get_page().
> - * So, we use get_page_unless_zero(), here. Even failed, page fault
> - * will occur again.
> - */
> - if (!get_page_unless_zero(page))
> - goto out;
> pte_unmap_unlock(ptep, ptl);
> - wait_on_page_locked(page);
> - put_page(page);
> + page_lock(page);
> + page_unlock(page);
> return;
> out:
> pte_unmap_unlock(ptep, ptl);

--
Michal Hocko
SUSE Labs

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