On Thu 03-01-19 11:38:31, Qian Cai wrote: > On 1/3/19 6:51 AM, Michal Hocko wrote: > > 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? > > As mentioned above, "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." Do you have any numbers to show how many allocation are we losing that way? In other words, do we care enough to create an ugly code? > >> 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? > > No, it is related. Because of this patch, page_ext_init() is called after all > the memory has already been initialized, > so no longer necessary to call early_pfn_to_nid(). Yes, but it looks like a follow up cleanup/optimization to me. -- Michal Hocko SUSE Labs
