On 3/6/24 13:32, Oscar Salvador wrote:
> Although the retrieval of the stack_records for {dummy,failure}_handle
> happen when page_owner gets initialized, there seems to be some situations
> where stackdepot space has been already depleted by then, so we get
> 0-handles which make stack_records being NULL for those cases.
>
> Be careful to 1) only bump stack_records refcount and 2) only access
> stack_record fields if we actually have a non-null stack_record between
> hands.
>
> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> Closes: https://lore.kernel.org/oe-lkp/202403051032.e2f865a-lkp@xxxxxxxxx
> Fixes: 4bedfb314bdd ("mm,page_owner: implement the tracking of the stacks count")
> Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
> mm/page_owner.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 033e349f6479..7163a1c44ccf 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -107,8 +107,10 @@ static __init void init_page_owner(void)
> /* Initialize dummy and failure stacks and link them to stack_list */
> dummy_stack.stack_record = __stack_depot_get_stack_record(dummy_handle);
> failure_stack.stack_record = __stack_depot_get_stack_record(failure_handle);
> - refcount_set(&dummy_stack.stack_record->count, 1);
> - refcount_set(&failure_stack.stack_record->count, 1);
> + if (dummy_stack.stack_record)
> + refcount_set(&dummy_stack.stack_record->count, 1);
> + if (failure_stack.stack_record)
> + refcount_set(&failure_stack.stack_record->count, 1);
> dummy_stack.next = &failure_stack;
> stack_list = &dummy_stack;
> }
> @@ -856,6 +858,9 @@ static int stack_print(struct seq_file *m, void *v)
> unsigned long nr_entries;
> struct stack_record *stack_record = stack->stack_record;
>
> + if (!stack->stack_record)
> + return 0;
> +
> nr_entries = stack_record->size;
> entries = stack_record->entries;
> stack_count = refcount_read(&stack_record->count) - 1;
