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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 <[email protected]>
Acked-by: Davidlohr Bueso <[email protected]>
Cc: Luiz Capitulino <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Acked-by: Hillf Danton <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
David Rientjes 2015-03-12 16:25:54 -07:00 • committed by Linus Torvalds
commit 44fc80573c
1 changed files with 3 additions and 1 deletions
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4
mm/hugetlb.c
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@ -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);
}
}