[PATCH AUTOSEL 4.20 38/52] Revert "mm: use early_pfn_to_nid in page_ext_init"

[Sasha Levin]

From: Qian Cai <cai@xxxxxx>

[ Upstream commit 2f1ee0913ce58efe7f18fbd518bd54c598559b89 ]

This reverts commit fe53ca54270a ("mm: use early_pfn_to_nid in
page_ext_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.

  UBSAN: Undefined behaviour in ./include/linux/mm.h:1104:50
  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

It did not handle it well in init_pages_in_zone() which ends up calling
page_to_nid().

  page:ffffea0004200000 is uninitialized and poisoned
  raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
  raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
  page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
  page_owner info is not active (free page?)
  kernel BUG at include/linux/mm.h:990!
  RIP: 0010:init_page_owner+0x486/0x520

This means that assumptions behind commit 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.

Link: http://lkml.kernel.org/r/20190115202812.75820-1-cai@xxxxxx
Signed-off-by: Qian Cai <cai@xxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Pasha Tatashin <Pavel.Tatashin@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Yang Shi <yang.shi@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 init/main.c   | 3 ++-
 mm/page_ext.c | 4 +---
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/init/main.c b/init/main.c
index ee147103ba1b..5def2b073b9c 100644
--- a/init/main.c
+++ b/init/main.c
@@ -695,7 +695,6 @@ asmlinkage __visible void __init start_kernel(void)
 		initrd_start = 0;
 	}
 #endif
-	page_ext_init();
 	kmemleak_init();
 	debug_objects_mem_init();
 	setup_per_cpu_pageset();
@@ -1147,6 +1146,8 @@ static noinline void __init kernel_init_freeable(void)
 	sched_init_smp();
 
 	page_alloc_init_late();
+	/* Initialize page ext after all struct pages are initialized. */
+	page_ext_init();
 
 	do_basic_setup();
 
diff --git a/mm/page_ext.c b/mm/page_ext.c
index ae44f7adbe07..8c78b8d45117 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -398,10 +398,8 @@ void __init page_ext_init(void)
 			 * We know some arch can have a nodes layout such as
 			 * -------------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;
-- 
2.19.1