Messages in this thread Patch in this message | | | Date | Tue, 24 Feb 2015 16:16:03 -0800 (PST) | From | David Rientjes <> | Subject | [patch] mm, hugetlb: close race when setting PageTail for gigantic pages |
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Now that gigantic pages are dynamically allocatable, care must be taken to ensure that p->first_page is valid before setting PageTail.
If this isn't done, then it is possible to race and have compound_head() return NULL.
Signed-off-by: David Rientjes <rientjes@google.com> --- mm/hugetlb.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -917,7 +917,6 @@ static void prep_compound_gigantic_page(struct page *page, unsigned long order) __SetPageHead(page); __ClearPageReserved(page); for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) { - __SetPageTail(p); /* * For gigantic hugepages allocated through bootmem at * boot, it's safer to be consistent with the not-gigantic @@ -933,6 +932,9 @@ static void prep_compound_gigantic_page(struct page *page, unsigned long order) __ClearPageReserved(p); set_page_count(p, 0); p->first_page = page; + /* Make sure p->first_page is always valid for PageTail() */ + smp_wmb(); + __SetPageTail(p); } }
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