hugetlb: fix race in alloc_fresh_huge_page()

That static `nid' index needs locking.  Without it we can end up calling
alloc_pages_node() with an illegal node ID and the kernel crashes.

Acked-by: gurudas pai <gurudas.pai@oracle.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 4 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index eaba7d6b25a0..acc0fb3cf067 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -101,13 +101,20 @@ static void free_huge_page(struct page *page)
 
 static int alloc_fresh_huge_page(void)
 {
-        static int nid = 0;
+        static int prev_nid;
         struct page *page;
-        page = alloc_pages_node(nid, GFP_HIGHUSER|__GFP_COMP|__GFP_NOWARN,
-                                        HUGETLB_PAGE_ORDER);
-        nid = next_node(nid, node_online_map);
+        static DEFINE_SPINLOCK(nid_lock);
+        int nid;
+
+        spin_lock(&nid_lock);
+        nid = next_node(prev_nid, node_online_map);
         if (nid == MAX_NUMNODES)
                 nid = first_node(node_online_map);
+        prev_nid = nid;
+        spin_unlock(&nid_lock);
+
+        page = alloc_pages_node(nid, GFP_HIGHUSER|__GFP_COMP|__GFP_NOWARN,
+                                        HUGETLB_PAGE_ORDER);
         if (page) {
                 set_compound_page_dtor(page, free_huge_page);
                 spin_lock(&hugetlb_lock);