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

[Mikhail Zaslonko <zaslonko@linux.ibm.com>]

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:

 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

Fix the problem by initializing the last memory section of the highest 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 | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2ec9cc407216..41ef5508e5f1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5542,6 +5542,21 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
 			cond_resched();
 		}
 	}
+#ifdef CONFIG_SPARSEMEM
+	/*
+	 * If there is no zone spanning 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).
+	 */
+	if (end_pfn == max_pfn) {
+		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
-- 
2.16.4