Re: [PATCH] mm/page_owner: fix for deferred struct page init

[Michal Hocko]

On Thu 20-12-18 01:03:03, Qian Cai wrote:
> When booting a system with "page_owner=on",
> 
> start_kernel
>   page_ext_init
>     invoke_init_callbacks
>       init_section_page_ext
>         init_page_owner
>           init_early_allocated_pages
>             init_zones_in_node
>               init_pages_in_zone
>                 lookup_page_ext
>                   page_to_nid
> 
> The issue here is that page_to_nid() will not work since some page
> flags have no node information until later in page_alloc_init_late() due
> to DEFERRED_STRUCT_PAGE_INIT. Hence, it could trigger an out-of-bounds
> access with an invalid nid.
> 
> [    8.666047] UBSAN: Undefined behaviour in ./include/linux/mm.h:1104:50
> [    8.672603] index 7 is out of range for type 'zone [5]'
> 
> Also, kernel will panic since flags were poisoned earlier with,
> 
> CONFIG_DEBUG_VM_PGFLAGS=y
> CONFIG_NODE_NOT_IN_PAGE_FLAGS=n
> 
> start_kernel
>   setup_arch
>     pagetable_init
>       paging_init
>         sparse_init
>           sparse_init_nid
>             memblock_alloc_try_nid_raw
> 
> Although later it tries to set page flags for pages in reserved bootmem
> regions,
> 
> mm_init
>   mem_init
>     memblock_free_all
>       free_low_memory_core_early
>         reserve_bootmem_region
> 
> there could still have some freed pages from the page allocator but yet
> to be initialized due to DEFERRED_STRUCT_PAGE_INIT. It have already been
> dealt with a bit in page_ext_init().

Is there any reason why we cannot postpone page_ext initialization to
after all the memory is initialized?
-- 
Michal Hocko
SUSE Labs