On Mon 20-01-20 08:19:09, Qian Cai wrote:
> It makes sense to call the WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE)
> from start_isolate_page_range(), but should avoid triggering it from
> userspace, i.e, from is_mem_section_removable() because it could be a
> DoS if warn_on_panic is set.
Let's just make it clear that this mostly a pre-cautious because a real
DoS should be pretty much impossible. But let's see whether somebody
want to make a CVE out of it ;)
> While at it, simplify the code a bit by removing an unnecessary jump
> label and a local variable, so set_migratetype_isolate() could really
> return a bool.
>
> Suggested-by: Michal Hocko <mhocko@xxxxxxxxxx>
> Signed-off-by: Qian Cai <cai@xxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Thanks!
> ---
>
> v2: Improve the commit log.
> Warn for all start_isolate_page_range() users not just offlining.
>
> mm/page_alloc.c | 11 ++++-------
> mm/page_isolation.c | 30 +++++++++++++++++-------------
> 2 files changed, 21 insertions(+), 20 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 621716a25639..3c4eb750a199 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8231,7 +8231,7 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
> if (is_migrate_cma(migratetype))
> return NULL;
>
> - goto unmovable;
> + return page;
> }
>
> for (; iter < pageblock_nr_pages; iter++) {
> @@ -8241,7 +8241,7 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
> page = pfn_to_page(pfn + iter);
>
> if (PageReserved(page))
> - goto unmovable;
> + return page;
>
> /*
> * If the zone is movable and we have ruled out all reserved
> @@ -8261,7 +8261,7 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
> unsigned int skip_pages;
>
> if (!hugepage_migration_supported(page_hstate(head)))
> - goto unmovable;
> + return page;
>
> skip_pages = compound_nr(head) - (page - head);
> iter += skip_pages - 1;
> @@ -8303,12 +8303,9 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
> * is set to both of a memory hole page and a _used_ kernel
> * page at boot.
> */
> - goto unmovable;
> + return page;
> }
> return NULL;
> -unmovable:
> - WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
> - return pfn_to_page(pfn + iter);
> }
>
> #ifdef CONFIG_CONTIG_ALLOC
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index e70586523ca3..31f5516f5d54 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -15,12 +15,12 @@
> #define CREATE_TRACE_POINTS
> #include <trace/events/page_isolation.h>
>
> -static int set_migratetype_isolate(struct page *page, int migratetype, int isol_flags)
> +static bool set_migratetype_isolate(struct page *page, int migratetype,
> + int isol_flags)
> {
> - struct page *unmovable = NULL;
> + struct page *unmovable = ERR_PTR(-EBUSY);
> struct zone *zone;
> unsigned long flags;
> - int ret = -EBUSY;
>
> zone = page_zone(page);
>
> @@ -49,21 +49,25 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
> NULL);
>
> __mod_zone_freepage_state(zone, -nr_pages, mt);
> - ret = 0;
> }
>
> out:
> spin_unlock_irqrestore(&zone->lock, flags);
> - if (!ret)
> +
> + if (!unmovable) {
> drain_all_pages(zone);
> - else if ((isol_flags & REPORT_FAILURE) && unmovable)
> - /*
> - * printk() with zone->lock held will guarantee to trigger a
> - * lockdep splat, so defer it here.
> - */
> - dump_page(unmovable, "unmovable page");
> -
> - return ret;
> + } else {
> + WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
> +
> + if ((isol_flags & REPORT_FAILURE) && !IS_ERR(unmovable))
> + /*
> + * printk() with zone->lock held will likely trigger a
> + * lockdep splat, so defer it here.
> + */
> + dump_page(unmovable, "unmovable page");
> + }
> +
> + return !!unmovable;
> }
>
> static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
> --
> 2.21.0 (Apple Git-122.2)
--
Michal Hocko
SUSE Labs
