From: liqiong <liqiong@xxxxxxxxxxxx> 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> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/migrate.c | 8 ++++++++ 1 file changed, 8 insertions(+) --- a/mm/migrate.c +++ b/mm/migrate.c @@ -472,6 +472,10 @@ int migrate_page_move_mapping(struct add 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(struc 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 || Patches currently in stable-queue which might be from liqiong@xxxxxxxxxxxx are queue-4.19/mm-fix-dereference-a-null-pointer-in-migrate_page_move_mapping.patch