[2.6.20.17 review 39/58] hugetlb: fix race in alloc_fresh_huge_page()

[Willy Tarreau]

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@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
Signed-off-by: Willy Tarreau <w@xxxxxx>
---
 mm/hugetlb.c |   15 +++++++++++----
 1 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 36db012..7c07eb2 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);
-- 
1.5.2.5

-- 
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