Re: [PATCH v3] mm/page_owner: fix for deferred struct page init

[Michal Hocko]

On Thu 20-12-18 15:31:56, 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().
> 
> * Take into account DEFERRED_STRUCT_PAGE_INIT.
> */
> if (early_pfn_to_nid(pfn) != nid)
> 	continue;
> 
> However, it did not handle it well in init_pages_in_zone() which end up
> calling page_to_nid().
> 
> [   11.917212] page:ffffea0004200000 is uninitialized and poisoned
> [   11.917220] raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff
> ffffffffffffffff
> [   11.921745] raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff
> ffffffffffffffff
> [   11.924523] page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
> [   11.926498] page_owner info is not active (free page?)
> [   12.329560] kernel BUG at include/linux/mm.h:990!
> [   12.337632] RIP: 0010:init_page_owner+0x486/0x520
> 
> Since there is no other routines depend on page_ext_init() in
> start_kernel(), just move it after page_alloc_init_late() to ensure that
> there is no deferred pages need to de dealt with. If deselected
> DEFERRED_STRUCT_PAGE_INIT, it is still better to call page_ext_init()
> earlier, so page owner could catch more early page allocation call
> sites. This gives us a good compromise between catching good and bad
> call sites (See the v1 patch [1]) in case of DEFERRED_STRUCT_PAGE_INIT.
> 
> [1] https://lore.kernel.org/lkml/20181220060303.38686-1-cai@xxxxxx/
> 
> Fixes: fe53ca54270 (mm: use early_pfn_to_nid in page_ext_init)
> Suggested-by: Michal Hocko <mhocko@xxxxxxxxxx>
> Signed-off-by: Qian Cai <cai@xxxxxx>
> ---
> 
> v3: still call page_ext_init() earlier if DEFERRED_STRUCT_PAGE_INIT=n.
> 
> v2: postpone page_ext_init() to after page_alloc_init_late().
> 
>  init/main.c   | 5 +++++
>  mm/page_ext.c | 3 +--
>  2 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/init/main.c b/init/main.c
> index 2b7b7fe173c9..5d9904370f76 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -696,7 +696,9 @@ asmlinkage __visible void __init start_kernel(void)
>  		initrd_start = 0;
>  	}
>  #endif
> +#ifndef CONFIG_DEFERRED_STRUCT_PAGE_INIT
>  	page_ext_init();
> +#endif
>  	kmemleak_init();
>  	setup_per_cpu_pageset();
>  	numa_policy_init();
> @@ -1147,6 +1149,9 @@ static noinline void __init kernel_init_freeable(void)
>  	sched_init_smp();
>  
>  	page_alloc_init_late();
> +#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
> +	page_ext_init();
> +#endif
>  
>  	do_basic_setup();

Is this really necessary? Why cannot we simply postpone page_ext_init
unconditioanally?

>  
> diff --git a/mm/page_ext.c b/mm/page_ext.c
> index ae44f7adbe07..d76fd51e312a 100644
> --- a/mm/page_ext.c
> +++ b/mm/page_ext.c
> @@ -399,9 +399,8 @@ void __init page_ext_init(void)
>  			 * -------------pfn-------------->
>  			 * N0 | N1 | N2 | N0 | N1 | N2|....
>  			 *
> -			 * Take into account DEFERRED_STRUCT_PAGE_INIT.
>  			 */
> -			if (early_pfn_to_nid(pfn) != nid)
> +			if (pfn_to_nid(pfn) != nid)
>  				continue;
>  			if (init_section_page_ext(pfn, nid))
>  				goto oom;

Also this doesn't seem to be related, right?
-- 
Michal Hocko
SUSE Labs