Commit 44fc8057 authored Mar 12, 2015 by David Rientjes Committed by Linus Torvalds Mar 12, 2015

mm, hugetlb: close race when setting PageTail for gigantic pages



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>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent e009d5dc

mm/hugetlb.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -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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