Re: [PATCH v2 1/1] mm, memory_hotplug: Initialize struct pages for the full memory section

David Hildenbrand
2018-12-14T15:22:14Z

On 12.12.18 18:27, Mikhail Zaslonko wrote:
> 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.
>
> Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
> Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
> Cc: <stable@vger.kernel.org>
> ---
> mm/page_alloc.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 2ec9cc407216..e2afdb2dc2c5 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5542,6 +5542,18 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
> 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++;

This page will not be marked as PG_reserved - although it is a physical
memory gap. Do we care?

> + }
> +#endif
> }
>
> #ifdef CONFIG_ZONE_DEVICE
>

--

Thanks,

David / dhildenb