2020-01-20 16:40:42

by Qian Cai

Subject: [PATCH -mm v3] mm/page_isolation: fix potential warning from user

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 crash
the system by a non-root user if warn_on_panic is set.

While at it, simplify the code a bit by removing an unnecessary jump
label.

Suggested-by: Michal Hocko <[email protected]>
Signed-off-by: Qian Cai <[email protected]>
---

v3: Drop the page_isolation.c cleanup change.
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 | 18 +++++++++++-------
2 files changed, 15 insertions(+), 14 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..a9fd7c740c23 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -54,14 +54,18 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_

out:
spin_unlock_irqrestore(&zone->lock, flags);
- if (!ret)
+ if (!ret) {
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");
+ } else {
+ WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
+
+ if ((isol_flags & REPORT_FAILURE) && unmovable)
+ /*
+ * printk() with zone->lock held will likely trigger a
+ * lockdep splat, so defer it here.
+ */
+ dump_page(unmovable, "unmovable page");
+ }

return ret;
}
--
2.21.0 (Apple Git-122.2)

2020-01-20 16:52:37

by David Hildenbrand

Subject: Re: [PATCH -mm v3] mm/page_isolation: fix potential warning from user

On 20.01.20 17:39, 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 crash
> the system by a non-root user if warn_on_panic is set.
>
> While at it, simplify the code a bit by removing an unnecessary jump
> label.
>
> Suggested-by: Michal Hocko <[email protected]>
> Signed-off-by: Qian Cai <[email protected]>
> ---
>
> v3: Drop the page_isolation.c cleanup change.
> 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 | 18 +++++++++++-------
> 2 files changed, 15 insertions(+), 14 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..a9fd7c740c23 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -54,14 +54,18 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
>
> out:
> spin_unlock_irqrestore(&zone->lock, flags);
> - if (!ret)
> + if (!ret) {
> 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");
> + } else {
> + WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
> +
> + if ((isol_flags & REPORT_FAILURE) && unmovable)
> + /*
> + * printk() with zone->lock held will likely trigger a
> + * lockdep splat, so defer it here.
> + */
> + dump_page(unmovable, "unmovable page");
> + }
>
> return ret;
> }
>

Thanks!

Reviewed-by: David Hildenbrand <[email protected]>

--
Thanks,

David / dhildenb

2020-01-20 17:19:22

by Michal Hocko

Subject: Re: [PATCH -mm v3] mm/page_isolation: fix potential warning from user

On Mon 20-01-20 11:39:15, 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 crash
> the system by a non-root user if warn_on_panic is set.
>
> While at it, simplify the code a bit by removing an unnecessary jump
> label.
>
> Suggested-by: Michal Hocko <[email protected]>
> Signed-off-by: Qian Cai <[email protected]>

Acked-by: Michal Hocko <[email protected]>

Thanks!

> ---
>
> v3: Drop the page_isolation.c cleanup change.
> 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 | 18 +++++++++++-------
> 2 files changed, 15 insertions(+), 14 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..a9fd7c740c23 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -54,14 +54,18 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
>
> out:
> spin_unlock_irqrestore(&zone->lock, flags);
> - if (!ret)
> + if (!ret) {
> 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");
> + } else {
> + WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
> +
> + if ((isol_flags & REPORT_FAILURE) && unmovable)
> + /*
> + * printk() with zone->lock held will likely trigger a
> + * lockdep splat, so defer it here.
> + */
> + dump_page(unmovable, "unmovable page");
> + }
>
> return ret;
> }
> --
> 2.21.0 (Apple Git-122.2)

--
Michal Hocko
SUSE Labs