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@vger.kernel.org # linux-4.19.y Signed-off-by: liqiong liqiong@nfschina.com --- 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 ||