Re: [PATCH v1 2/6] mm/page_isolation: don't dump_page(NULL) in set_migratetype_isolate()

Baoquan He
2020-07-28T13:57:02Z

On 06/30/20 at 04:26pm, David Hildenbrand wrote:
> Right now, if we have two isolations racing, we might trigger the
> WARN_ON_ONCE() and to dump_page(NULL), dereferencing NULL. Let's just
> return directly.
>
> In the future, we might want to report -EAGAIN to the caller instead, as
> this could indicate a temporary isolation failure only.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> mm/page_isolation.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index f6d07c5f0d34d..553b49a34cf71 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -29,10 +29,12 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
> /*
> * We assume the caller intended to SET migrate type to isolate.
> * If it is already set, then someone else must have raced and
> - * set it before us. Return -EBUSY
> + * set it before us.
> */
> - if (is_migrate_isolate_page(page))
> - goto out;
> + if (is_migrate_isolate_page(page)) {
> + spin_unlock_irqrestore(&zone->lock, flags);
> + return -EBUSY;

Good catch, the fix looks good to me.

Reviewed-by: Baoquan He <bhe@redhat.com>

> + }
>
> /*
> * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself.
> --
> 2.26.2
>
>