[PATCH 3.16 104/306] mm/hugetlb: check for reserved hugepages during memory offline

Ben Hutchings
2017-02-15T23:33:10Z

From: Gerald Schaefer <gerald.schaefer@de.ibm.com>

commit 082d5b6b60e9f25e1511557fcfcb21eedd267446 upstream.

In dissolve_free_huge_pages(), free hugepages will be dissolved without
making sure that there are enough of them left to satisfy hugepage
reservations.

Fix this by adding a return value to dissolve_free_huge_pages() and
checking h->free_huge_pages vs. h->resv_huge_pages. Note that this may
lead to the situation where dissolve_free_huge_page() returns an error
and all free hugepages that were dissolved before that error are lost,
while the memory block still cannot be set offline.

Fixes: c8721bbb ("mm: memory-hotplug: enable memory hotplug to handle hugepage")
Link: http://lkml.kernel.org/r/20160926172811.94033-3-gerald.schaefer@de.ibm.com
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Rui Teng <rui.teng@linux.vnet.ibm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
include/linux/hugetlb.h | 6 +++---
mm/hugetlb.c | 26 +++++++++++++++++++++-----
mm/memory_hotplug.c | 4 +++-
3 files changed, 27 insertions(+), 9 deletions(-)

--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -396,8 +396,8 @@ static inline pgoff_t basepage_index(str
return __basepage_index(page);
}

-extern void dissolve_free_huge_pages(unsigned long start_pfn,
- unsigned long end_pfn);
+extern int dissolve_free_huge_pages(unsigned long start_pfn,
+ unsigned long end_pfn);
static inline int hugepage_migration_supported(struct hstate *h)
{
#ifdef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
@@ -452,7 +452,7 @@ static inline pgoff_t basepage_index(str
{
return page->index;
}
-#define dissolve_free_huge_pages(s, e) do {} while (0)
+#define dissolve_free_huge_pages(s, e) 0
#define hugepage_migration_supported(h) 0

static inline spinlock_t *huge_pte_lockptr(struct hstate *h,
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1067,21 +1067,31 @@ static int free_pool_huge_page(struct hs

/*
* Dissolve a given free hugepage into free buddy pages. This function does
- * nothing for in-use (including surplus) hugepages.
+ * nothing for in-use (including surplus) hugepages. Returns -EBUSY if the
+ * number of free hugepages would be reduced below the number of reserved
+ * hugepages.
*/
-static void dissolve_free_huge_page(struct page *page)
+static int dissolve_free_huge_page(struct page *page)
{
+ int rc = 0;
+
spin_lock(&hugetlb_lock);
if (PageHuge(page) && !page_count(page)) {
struct page *head = compound_head(page);
struct hstate *h = page_hstate(head);
int nid = page_to_nid(head);
+ if (h->free_huge_pages - h->resv_huge_pages == 0) {
+ rc = -EBUSY;
+ goto out;
+ }
list_del(&head->lru);
h->free_huge_pages--;
h->free_huge_pages_node[nid]--;
update_and_free_page(h, head);
}
+out:
spin_unlock(&hugetlb_lock);
+ return rc;
}

/*
@@ -1089,16 +1099,22 @@ static void dissolve_free_huge_page(stru
* make specified memory blocks removable from the system.
* Note that this will dissolve a free gigantic hugepage completely, if any
* part of it lies within the given range.
+ * Also note that if dissolve_free_huge_page() returns with an error, all
+ * free hugepages that were dissolved before that error are lost.
*/
-void dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)
+int dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)
{
unsigned long pfn;
+ int rc = 0;

if (!hugepages_supported())
- return;
+ return rc;

for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << minimum_order)
- dissolve_free_huge_page(pfn_to_page(pfn));
+ if (rc = dissolve_free_huge_page(pfn_to_page(pfn)))
+ break;
+
+ return rc;
}

static struct page *alloc_buddy_huge_page(struct hstate *h, int nid)
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1732,7 +1732,9 @@ repeat:
* dissolve free hugepages in the memory block before doing offlining
* actually in order to make hugetlbfs's object counting consistent.
*/
- dissolve_free_huge_pages(start_pfn, end_pfn);
+ ret = dissolve_free_huge_pages(start_pfn, end_pfn);
+ if (ret)
+ goto failed_removal;
/* check again */
offlined_pages = check_pages_isolated(start_pfn, end_pfn);
if (offlined_pages < 0) {