Upstream doesn't use radix tree any more in migrate.c, no need this patch.
The two functions look up a slot and dereference the pointer,
If the pointer is null, the kernel would crash and dump.
The 'numad' service calls 'migrate_pages' periodically. If some slots
being replaced (Cache Eviction), the radix_tree_lookup_slot() returns
a null pointer that causes kernel crash.
"numad": crash> bt
[exception RIP: migrate_page_move_mapping+337]
Introduce pointer checking to avoid dereference a null pointer.
Cc: <stable@xxxxxxxxxxxxxxx> # linux-4.19.y
Signed-off-by: liqiong <liqiong@xxxxxxxxxxxx>
---
mm/migrate.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/mm/migrate.c b/mm/migrate.c
index a69b842f95da..76f8dedc0e02 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -472,6 +472,10 @@ int migrate_page_move_mapping(struct address_space *mapping,
pslot = radix_tree_lookup_slot(&mapping->i_pages,
page_index(page));
+ if (pslot == NULL) {
+ xa_unlock_irq(&mapping->i_pages);
+ return -EAGAIN;
+ }
expected_count += hpage_nr_pages(page) + page_has_private(page);
if (page_count(page) != expected_count ||
@@ -590,6 +594,10 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
xa_lock_irq(&mapping->i_pages);
pslot = radix_tree_lookup_slot(&mapping->i_pages, page_index(page));
+ if (pslot == NULL) {
+ xa_unlock_irq(&mapping->i_pages);
+ return -EAGAIN;
+ }
expected_count = 2 + page_has_private(page);
if (page_count(page) != expected_count ||
--
2.25.1
