[PATCH 1/1] mm/hugetlb: fix memory offline with hugepage size > memory block size

Gerald Schaefer
2016-09-20T15:54:34Z

dissolve_free_huge_pages() will either run into the VM_BUG_ON() or a
list corruption and addressing exception when trying to set a memory
block offline that is part (but not the first part) of a gigantic
hugetlb page with a size > memory block size.

When no other smaller hugepage sizes are present, the VM_BUG_ON() will
trigger directly. In the other case we will run into an addressing
exception later, because dissolve_free_huge_page() will not use the head
page of the compound hugetlb page which will result in a NULL hstate
from page_hstate(). list_del() would also not work well on a tail page.

To fix this, first remove the VM_BUG_ON() because it is wrong, and then
use the compound head page in dissolve_free_huge_page().

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
---
mm/hugetlb.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 87e11d8..65e723c 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1441,15 +1441,17 @@ static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
*/
static void dissolve_free_huge_page(struct page *page)
{
+ struct page *head = compound_head(page);
+
spin_lock(&hugetlb_lock);
- if (PageHuge(page) && !page_count(page)) {
- struct hstate *h = page_hstate(page);
- int nid = page_to_nid(page);
- list_del(&page->lru);
+ if (!page_count(head)) {
+ struct hstate *h = page_hstate(head);
+ int nid = page_to_nid(head);
+ list_del(&head->lru);
h->free_huge_pages--;
h->free_huge_pages_node[nid]--;
h->max_huge_pages--;
- update_and_free_page(h, page);
+ update_and_free_page(h, head);
}
spin_unlock(&hugetlb_lock);
}
@@ -1466,9 +1468,9 @@ void dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)
if (!hugepages_supported())
return;

- VM_BUG_ON(!IS_ALIGNED(start_pfn, 1 << minimum_order));
for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << minimum_order)
- dissolve_free_huge_page(pfn_to_page(pfn));
+ if (PageHuge(pfn_to_page(pfn)))
+ dissolve_free_huge_page(pfn_to_page(pfn));
}

/*
--
2.8.4