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Subject[PATCH -mm v2] mm/page_isolation: fix potential warning from user
Date
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.

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@kernel.org>
Signed-off-by: Qian Cai <cai@lca.pw>
---

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)
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