[PATCH 3.15 32/37] mm: hugetlb: fix copy_hugetlb_page_range()

Greg Kroah-Hartman
2014-07-30T01:49:08Z

From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

commit 0253d634e0803a8376a0d88efee0bf523d8673f9 upstream.

Commit 4a705fef9862 ("hugetlb: fix copy_hugetlb_page_range() to handle
migration/hwpoisoned entry") changed the order of
huge_ptep_set_wrprotect() and huge_ptep_get(), which leads to breakage
in some workloads like hugepage-backed heap allocation via libhugetlbfs.
This patch fixes it.

The test program for the problem is shown below:

$ cat heap.c
#include <unistd.h>
#include <stdlib.h>
#include <string.h>

#define HPS 0x200000

int main() {
int i;
char *p = malloc(HPS);
memset(p, '1', HPS);
for (i = 0; i < 5; i++) {
if (!fork()) {
memset(p, '2', HPS);
p = malloc(HPS);
memset(p, '3', HPS);
free(p);
return 0;
}
}
sleep(1);
free(p);
return 0;
}

$ export HUGETLB_MORECORE=yes ; export HUGETLB_NO_PREFAULT= ; hugectl --heap ./heap

Fixes 4a705fef9862 ("hugetlb: fix copy_hugetlb_page_range() to handle
migration/hwpoisoned entry"), so is applicable to -stable kernels which
include it.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reported-by: Guillaume Morin <guillaume@morinfr.org>
Suggested-by: Guillaume Morin <guillaume@morinfr.org>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/hugetlb.c | 1 +
1 file changed, 1 insertion(+)

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2461,6 +2461,7 @@ int copy_hugetlb_page_range(struct mm_st
} else {
if (cow)
huge_ptep_set_wrprotect(src, addr, src_pte);
+ entry = huge_ptep_get(src_pte);
ptepage = pte_page(entry);
get_page(ptepage);
page_dup_rmap(ptepage);