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Qian Cai authored
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. This means that assumptions behind fe53ca54 ("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. [1] https://lore.kernel.org/lkml/20181220060303.38686-1-cai@lca.pw/ [mhocko@kernel.org: changelog addition] Link: http://lkml.kernel.org/r/20181220203156.43441-1-cai@lca.pw Fixes: fe53ca54 ("mm: use early_pfn_to_nid in page_ext_init") Signed-off-by:Qian Cai <cai@lca.pw> Suggested-by:
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