From: Mikhail Zaslonko zaslonko@linux.ibm.com Subject: mm, memory_hotplug: initialize struct pages for the full memory section

If memory end is not aligned with the sparse memory section boundary, the mapping of such a section is only partly initialized. This may lead to VM_BUG_ON due to uninitialized struct page access from is_mem_section_removable() or test_pages_in_a_zone() function triggered by memory_hotplug sysfs handlers:

Here are the the panic examples: CONFIG_DEBUG_VM=y CONFIG_DEBUG_VM_PGFLAGS=y

kernel parameter mem=2050M -------------------------- page:000003d082008000 is uninitialized and poisoned page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p)) Call Trace: ([<0000000000385b26>] test_pages_in_a_zone+0xde/0x160) [<00000000008f15c4>] show_valid_zones+0x5c/0x190 [<00000000008cf9c4>] dev_attr_show+0x34/0x70 [<0000000000463ad0>] sysfs_kf_seq_show+0xc8/0x148 [<00000000003e4194>] seq_read+0x204/0x480 [<00000000003b53ea>] __vfs_read+0x32/0x178 [<00000000003b55b2>] vfs_read+0x82/0x138 [<00000000003b5be2>] ksys_read+0x5a/0xb0 [<0000000000b86ba0>] system_call+0xdc/0x2d8 Last Breaking-Event-Address: [<0000000000385b26>] test_pages_in_a_zone+0xde/0x160 Kernel panic - not syncing: Fatal exception: panic_on_oops

kernel parameter mem=3075M -------------------------- page:000003d08300c000 is uninitialized and poisoned page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p)) Call Trace: ([<000000000038596c>] is_mem_section_removable+0xb4/0x190) [<00000000008f12fa>] show_mem_removable+0x9a/0xd8 [<00000000008cf9c4>] dev_attr_show+0x34/0x70 [<0000000000463ad0>] sysfs_kf_seq_show+0xc8/0x148 [<00000000003e4194>] seq_read+0x204/0x480 [<00000000003b53ea>] __vfs_read+0x32/0x178 [<00000000003b55b2>] vfs_read+0x82/0x138 [<00000000003b5be2>] ksys_read+0x5a/0xb0 [<0000000000b86ba0>] system_call+0xdc/0x2d8 Last Breaking-Event-Address: [<000000000038596c>] is_mem_section_removable+0xb4/0x190 Kernel panic - not syncing: Fatal exception: panic_on_oops

Fix the problem by initializing the last memory section of each zone in memmap_init_zone() till the very end, even if it goes beyond the zone end.

Michal said:

: This has alwways been problem AFAIU. It just went unnoticed because we : have zeroed memmaps during allocation before f7f99100d8d9 ("mm: stop : zeroing memory during allocation in vmemmap") and so the above test : would simply skip these ranges as belonging to zone 0 or provided a : garbage. : : So I guess we do care for post f7f99100d8d9 kernels mostly and : therefore Fixes: f7f99100d8d9 ("mm: stop zeroing memory during : allocation in vmemmap")

Link: http://lkml.kernel.org/r/20181212172712.34019-2-zaslonko@linux.ibm.com Fixes: f7f99100d8d9 ("mm: stop zeroing memory during allocation in vmemmap") Signed-off-by: Mikhail Zaslonko zaslonko@linux.ibm.com Reviewed-by: Gerald Schaefer gerald.schaefer@de.ibm.com Suggested-by: Michal Hocko mhocko@kernel.org Acked-by: Michal Hocko mhocko@suse.com Reported-by: Mikhail Gavrilov mikhail.v.gavrilov@gmail.com Tested-by: Mikhail Gavrilov mikhail.v.gavrilov@gmail.com Cc: Dave Hansen dave.hansen@intel.com Cc: Alexander Duyck alexander.h.duyck@linux.intel.com Cc: Pasha Tatashin Pavel.Tatashin@microsoft.com Cc: Martin Schwidefsky schwidefsky@de.ibm.com Cc: Heiko Carstens heiko.carstens@de.ibm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/page_alloc.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)

--- a/mm/page_alloc.c~mm-memory_hotplug-initialize-struct-pages-for-the-full-memory-section +++ a/mm/page_alloc.c @@ -5542,6 +5542,18 @@ void __meminit memmap_init_zone(unsigned cond_resched(); } } +#ifdef CONFIG_SPARSEMEM + /* + * If the zone does not span the rest of the section then + * we should at least initialize those pages. Otherwise we + * could blow up on a poisoned page in some paths which depend + * on full sections being initialized (e.g. memory hotplug). + */ + while (end_pfn % PAGES_PER_SECTION) { + __init_single_page(pfn_to_page(end_pfn), end_pfn, zone, nid); + end_pfn++; + } +#endif }

#ifdef CONFIG_ZONE_DEVICE _