mm/hugetlb: check for reserved hugepages during memory offline

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>

2 files changed, 24 insertions, 6 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 603bdd01ec2c..91ae1f567997 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1437,22 +1437,32 @@ static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
 
 /*
  * 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]--;
                 h->max_huge_pages--;
                 update_and_free_page(h, head);
         }
+out:
         spin_unlock(&hugetlb_lock);
+        return rc;
 }
 
 /*
@@ -1460,16 +1470,22 @@ static void dissolve_free_huge_page(struct page *page)
  * 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;
 }
 
 /*
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 9d29ba0f7192..962927309b6e 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1945,7 +1945,9 @@ 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) {