[PATCH v3 1/6] mm/page_isolation: don't dump_page(NULL) in set_migratetype_isolate()

David Hildenbrand
2020-08-04T07:24:32Z

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.

Reviewed-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Fixes: 4a55c0474a92 ("mm/hotplug: silence a lockdep splat with printk()")
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
mm/page_isolation.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index f6d07c5f0d34d..7d7d263ce7f4b 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;
+ }

/*
* FIXME: Now, memory hotplug doesn't call shrink_slab() by itself.
@@ -52,7 +54,6 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
ret = 0;
}

-out:
spin_unlock_irqrestore(&zone->lock, flags);
if (!ret) {
drain_all_pages(zone);
--
2.26.2