Re: [PATCH v2] mm/page_owner: fix for deferred struct page init

Michal Hocko
2019-01-09T07:34:14Z

On Thu 20-12-18 13:50:31, 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() and no real benefit to call it so early, just move it
> after page_alloc_init_late() to ensure that there is no deferred pages
> need to de dealt with.

The last paragraph should be updated. I would propose something like
this.

"
This means that assumptions behind fe53ca54270a ("mm: use
early_pfn_to_nid in page_ext_init") are incomplete. Therefore revert the
commit for now. A proper way to move the page_owner initialization to
sooner is to hook into memmap initialization.
"
>

Fixes: fe53ca54270a ("mm: use early_pfn_to_nid in page_ext_init")

> Suggested-by: Michal Hocko <mhocko@kernel.org>
> Signed-off-by: Qian Cai <cai@lca.pw>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>
> v2: postpone init_page_ext() to after page_alloc_init_late().
>
> init/main.c | 2 +-
> mm/page_ext.c | 3 +--
> 2 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/init/main.c b/init/main.c
> index 2b7b7fe173c9..1aeb062b2cb7 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -696,7 +696,6 @@ asmlinkage __visible void __init start_kernel(void)
> initrd_start = 0;
> }
> #endif
> - page_ext_init();
> kmemleak_init();
> setup_per_cpu_pageset();
> numa_policy_init();
> @@ -1147,6 +1146,7 @@ static noinline void __init kernel_init_freeable(void)
> sched_init_smp();
>
> page_alloc_init_late();
> + page_ext_init();
>
> do_basic_setup();
>
> 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;
> --
> 2.17.2 (Apple Git-113)

--
Michal Hocko
SUSE Labs