[PATCH] hugetlb: call arch_prepare_hugepage() for surplus pages

[Gerald Schaefer]

From: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx>

The s390 software large page emulation implements shared page tables
by using page->index of the first tail page from a compound large page
to store page table information. This is set up in arch_prepare_hugepage(),
which is called from alloc_fresh_huge_page_node().

A similar call to arch_prepare_hugepage() is missing for surplus large
pages that are allocated in alloc_buddy_huge_page(), which breaks the
software emulation mode for (surplus) large pages on s390. This patch
adds the missing call to arch_prepare_hugepage(). It will have no effect
on other architectures where arch_prepare_hugepage() is a nop.

Acked-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Signed-off-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx>
---

 mm/hugetlb.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

Index: linux/mm/hugetlb.c
===================================================================
--- linux.orig/mm/hugetlb.c
+++ linux/mm/hugetlb.c
@@ -565,7 +565,7 @@ static struct page *alloc_fresh_huge_pag
 		huge_page_order(h));
 	if (page) {
 		if (arch_prepare_hugepage(page)) {
-			__free_pages(page, HUGETLB_PAGE_ORDER);
+			__free_pages(page, huge_page_order(h));
 			return NULL;
 		}
 		prep_new_huge_page(h, page, nid);
@@ -665,6 +665,11 @@ static struct page *alloc_buddy_huge_pag
 					__GFP_REPEAT|__GFP_NOWARN,
 					huge_page_order(h));
 
+	if (page && arch_prepare_hugepage(page)) {
+		__free_pages(page, huge_page_order(h));
+		return NULL;
+	}
+
 	spin_lock(&hugetlb_lock);
 	if (page) {
 		/*

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