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

[Andrew Morton]

It's unclear (to me) where we stand with this patch.  Shold we proceed
with v3 for now, or is something else planned?


From: Qian Cai <cai@xxxxxx>
Subject: mm/page_owner: fix for deferred struct page init

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/

Link: http://lkml.kernel.org/r/20181220203156.43441-1-cai@xxxxxx
Fixes: fe53ca54270 (mm: use early_pfn_to_nid in page_ext_init)
Signed-off-by: Qian Cai <cai@xxxxxx>
Suggested-by: Michal Hocko <mhocko@xxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Pasha Tatashin <Pavel.Tatashin@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Yang Shi <yang.shi@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 init/main.c   |    5 +++++
 mm/page_ext.c |    3 +--
 2 files changed, 6 insertions(+), 2 deletions(-)

--- a/init/main.c~mm-page_owner-fix-for-deferred-struct-page-init
+++ a/init/main.c
@@ -695,7 +695,9 @@ asmlinkage __visible void __init start_k
 		initrd_start = 0;
 	}
 #endif
+#ifndef CONFIG_DEFERRED_STRUCT_PAGE_INIT
 	page_ext_init();
+#endif
 	kmemleak_init();
 	setup_per_cpu_pageset();
 	numa_policy_init();
@@ -1131,6 +1133,9 @@ static noinline void __init kernel_init_
 	sched_init_smp();
 
 	page_alloc_init_late();
+#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
+	page_ext_init();
+#endif
 
 	do_basic_setup();
 
--- a/mm/page_ext.c~mm-page_owner-fix-for-deferred-struct-page-init
+++ a/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;
_